A 3-dimensional finite element analysis to evaluate the impact of force direction, insertion angle, and cortical bone thickness on mini-screw and its surrounding bone

Background. The present study aimed to assess the stress and strain distribution on mini-screws and the surrounding bone in cases of different cortical bone thicknesses (CBTs), mini-screw insertion angles, and force directions using finite element analysis (FEA). Methods. Inventor professional version 8 software was used to construct 24 three-dimensional assemblies of mini-screws inserted with different insertion angles (30º, 60º, and 90º) in alveolar bone blocks with different CBTs (0.5, 1, 1.5, and 2 mm). The models simulated mini-screws inserted in bones with different CBTs and different insertion angles. A 2-N load was applied in two directions to mini-screw heads. The resultant stresses of the applied load were collected from the output of the ANSYS program. Results. The results indicated that force direction affected bone strains as the horizontal force generated more strains on cortical bone than the oblique one. Force applied to 60º inserted mini-screws generated much more strains on cortical bone than 90º and 30º inserted mini-screws. In a 60º inserted mini-screw, the horizontal force generated about 45% more strains on cortical bone than the oblique one. The exerted microstrain on bone decreased as CBT increased. Conclusion. It can be concluded that inserting mini-screws at 60º to the bone surface should be avoided as it generates much more strains on cortical bone than 90º and 30º, especially when a force parallel to the bone surface is applied.

Sensing small interaction forces through proprioception

Understanding the human motor control strategy during physical interaction tasks is crucial for developing future robots for physical human–robot interaction (pHRI). In physical human–human interaction (pHHI), small interaction forces are known to convey their intent between the partners for effective motor communication. The aim of this work is to investigate what affects the human’s sensitivity to the externally applied interaction forces. The hypothesis is that one way the small interaction forces are sensed is through the movement of the arm and the resulting proprioceptive signals. A pHRI setup was used to provide small interaction forces to the hand of seated participants in one of four directions, while the participants were asked to identify the direction of the push while blindfolded. The result shows that participants’ ability to correctly report the direction of the interaction force was lower with low interaction force as well as with high muscle contraction. The sensitivity to the interaction force direction increased with the radial displacement of the participant’s hand from the initial position: the further they moved the more correct their responses were. It was also observed that the estimated stiffness of the arm varies with the level of muscle contraction and robot interaction force.

The dynamics of touch sensing studied in a mass-spring-damper model of the skin

It has been shown that the skin can provide highly resolvable, dynamic tactile information to the central nervous system. However, currently available skin models do not provide a matching level of dynamic complexity. Motivated by recent observations that everyday interactions create a diversity of widespread travelling waves of multiple overlaid frequencies in the skin, we here model the skin as a 3D-distributed mass-spring-damper model. Shear forces across each spring were reported back as separate sources of information, on which we performed information content analysis using principal component analysis. We found that a wide range of settings of spring constants, dampening coefficients and baseline tension resulted in highly resolvable dynamic information even for simple skin-object interactions. Optimization showed that there were some settings that were more beneficial for a higher temporal resolution, i.e. where multiple independent interactions could be more easily resolved temporally. Whereas even a single sensor reporting a skin shear force with infinite precision by itself can achieve infinite resolution, biological sensors are noisy. We therefore also analyzed the resolution of force direction in the dynamic skin model, when their simulated signal-to-noise ratio was varied. We conclude that biological skin due to its inherent dynamics can afford a low spatial resolution of sensors (subsampling) while still maintaining a very high resolution for detecting skin-object interaction dynamics, and that biological evolution moreover due to this construct likely has been free to play around with a variety of mechanical skin parameters and sensor densities without significantly compromising this resolution.

The VISTA Approach in Canine Disimpaction

Canine disimpaction is always a challenging orthodontic treatment overall, even when the impacted permanent canine is in a high position, especially when in tight relation with the upper incisors’ roots. Conventional treatment methods are usually not capable of performing the correct force direction, consisting of the contemporary movement in the distal and vestibular directions of the canine crown, often provoking, as side effects, the presence of decubitus on the mucous of the lips and cheeks or a poor final appearance of the periodontal support of the disimpacted canine. Among the different approaches, the vertical incision subperiosteal tunnel access (VISTA) technique shows good performance with regard to the direction of the forces and the canine’s periodontal conditions when erupted; it is usually realized through an elastic chain connected to a temporary anchorage device (TAD) in the posterior area. In this paper, a different protocol for the VISTA method is also presented, to be resorted to in cases of difficult miniscrew positioning due to the anatomic conditions or stage of dentitions. The new protocol also considers the use of nickel–titanium coil springs in order to avoid the need of frequent reactivation of the device and consequent patient discomfort, highlighting its advantages and indications with respect to the traditional approach.

Mechanical properties of multi-materials porous structures based on triply periodic minimal surface fabricated by additive manufacturing

Purpose The purpose of this study is focused on the mechanical properties of multi-materials porous structures manufactured by selective laser melting (SLM). Design/methodology/approach The Diamond structure was designed by the triply periodic minimal surface function in MATLAB, and multi-materials porous structures were manufactured by SLM. Compression tests were applied to analyze the anisotropy of mechanical properties of multi-materials porous structures. Findings Compression results show that the multi-materials porous structure has a strong anisotropy behavior. When the compression force direction is parallel to the material arrangement, multi-materials porous structure was compressed in a layer-by-layer way, which is the traditional deformation of the gradient structure. However, when the compression force direction is perpendicular to the material arrangement, the compression curves show a near-periodic saw-tooth waveform characteristic, and this kind of structure was compressed consistently. It is demonstrated that the combination with high strength brittle material and low strength plastic material improves compression mode, and plastic material plays a role in buffering fracture. Originality/value This research provides a new method for the design and manufacturing of multi-materials porous structures and an approach to change the compression behavior of the porous structure.

Numerical study of the switching mechanism of a jet valve using the meshless method

This study numerically investigates fluid dynamics of a jet flow at supersonic speed. The meshless method and the overlapping point cloud method are used to handle the moving boundary problems. The interaction between the jet flow and a moving ball-shaped plug is numerically solved, which has been rarely done in the published literature. The switching mechanism of a novel designed jet valve in an attitude and orbit control system (AOCS) is analyzed. It is found out that applied pressure to the control inlets of the jet valve must be high enough in order to successfully drive the plug to move and subsequently change the force direction acting on the jet valve. Then the switching mechanism of AOCS can be triggered. The initial fluid condition also plays a vital role and it significantly influences the response time of the switch. This study explores the underlying physics of the jet flow on its deflection, wall attachment, and interaction with the ball-shaped plug. It contributes to the optimization design of the jet valve in the AOCS with a fast and efficient response.

Tactile Interaction Sensor with Millimeter Sensing Acuity

In this article we report on a 3 × 3 mm tactile interaction sensor that is able to simultaneously detect pressure level, pressure distribution, and shear force direction. The sensor consists of multiple mechanical switches under a conducting diaphragm. An external stimulus is measured by the deflection of the diaphragm and the arrangement of mechanical switches, resulting in low noise, high reliability, and high uniformity. Our sensor is able to detect tactile forces as small as ~50 mgf along with the direction of the shear force. It also distinguishes whether there is a normal pressure during slip motion. We also succeed in detecting the contact shape and the contact motion, demonstrating potential applications in robotics and remote input interfaces. Since our sensor has a simple structure and its function depends only on sensor dimensions, not on an active sensing material, in comparison with previous tactile sensors, our sensor shows high uniformity and reliability for an array-type integration.

Measurement of Aerodynamic Characteristics Using Cinder Models through Free Fall Experiment

Rocks ejected from a volcanic eruption often cause loss of lives and structures. Aerodynamic characteristics are needed for evaluating motions of volcanic rocks for the reduction of damage. Falling motions of volcanic rock were measured by using models imitated the configuration of cinders collected at the site of the experiment, Sakurajima volcano. Two types, one with sharp edges and one without sharp edges, were selected as representative of cinder and a sphere was selected as reference model. The falling motions of the models dropped down from a drone were recorded by video camera and a stand-alone measuring system that included a pressure sensor, acceleration and angular velocity sensors in the models. The motion, posture, velocity and acceleration of the model were obtained in order to measure the three-dimensional falling trajectory. The drag and the deviation angle between relative wind direction and wind force direction were examined. The variation of the drag coefficient and the deviation angle with Reynolds number was clarified.

Analysis of the Magnus Moment Aerodynamic Characteristics of Rotating Missiles at High Altitudes

The Magnus moment characteristics of rotating missiles with Mach numbers of 1.3 and 1.5 at different altitudes and angles of attack were numerically simulated based on the transition SST model. It was found that the Magnus moment direction of the missiles changed with the increase of the angle of attack. At a low altitude, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative; however, at high altitudes, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative and then again to positive. The Magnus force direction did not change with the change of the altitude and the angle of attack at low angles of attack; however, it changed with altitude at an angle of attack of 30°. When the angle of attack was 20°, the interference of the tail fin to the lateral force of the missile body was different from that for other angles of attack, leading to an increase of the lateral force of the rear part of the missile body. With the increasing altitude, the position of the boundary layer with a larger thickness of the missile body moved forward, making the lateral force distribution of the missile body even. Consequently, Magnus moments generated by different boundary layer thicknesses at the front and rear of the missile body decreased and the Magnus moment generated by the tail fin became larger. As lateral force directions of the missile body and the tail were opposite, the Magnus moment direction changed noticeably. Under a high angle of attack, the Magnus moment direction of the missile body changed with the increasing altitude. The absolute value of the pitch moment coefficient of the missile body decreased with the increasing altitude.