Measurement Of Contact Pressure Research Articles

Modeling of interlayer contact and contact pressure during fused filament fabrication

An in-line rheometer and data acquisition system are used to monitor the melt pressure, melt temperature, and environmental temperatures while producing parts via fused filament fabrication (FFF). Melt pressures are observed to increase when printing parts with small layer heights, which is attributed to the confined space created between the nozzle and the previous layer (i.e., an exit pressure). These exit pressures (referred to as contact pressure) and the resulting interlayer contact areas are analyzed for 2863 layers created at 21 different processing conditions. The measured contact pressure was found to directly influence the shape of the layers and the resulting interlayer contact. An intimate contact model based on contact pressure is combined with a wetting model to accurately predict the interlayer contact of FFF parts. This pressure-driven intimate contact model for FFF shows strong agreement with the observed interlayer contact. No theoretical model has previously existed for predicting interlayer contact, so this research provides a critical component for developing a comprehensive part strength model. Both the measurements and proposed model are sufficiently simple and accurate for real-time analysis of FFF quality, so the described in-line sensors provide valuable quality insights and are recommended for future researchers, printer manufacturers, and end-users.

A Flexible and Highly Sensitive Inductive Pressure Sensor Array Based on Ferrite Films.

There is a rapid growing demand for highly sensitive, easy adaptive and low-cost pressure sensing solutions in the fields of health monitoring, wearable electronics and home care. Here, we report a novel flexible inductive pressure sensor array with ultrahigh sensitivity and a simple construction, for large-area contact pressure measurements. In general, the device consists of three layers: a planar spiral inductor layer and ferrite film units attached on a polyethylene terephthalate (PET) membrane, which are separated by an array of elastic pillars. Importantly, by introducing the ferrite film with an excellent magnetic permeability, the effective permeability around the inductor is greatly influenced by the separation distance between the inductor and the ferrite film. As a result, the value of the inductance changes largely as the separation distance varies as an external load applies. Our device has achieved an ultrahigh sensitivity of 1.60 kPa−1 with a resolution of 13.61 Pa in the pressure range of 0–0.18 kPa, which is comparable to the current state-of-the-art flexible pressure sensors. More remarkably, our device shows an outstanding stability when exposed to environmental interferences, e.g., electrical noises from skin surfaces (within 0.08% variations) and a constant pressure load for more than 32 h (within 0.3% variations). In addition, the device exhibits a fast response time of 111 ms and a good repeatability under cyclic pressures varying from 38.45 to 177.82 Pa. To demonstrate its practical usage, we have successfully developed a 4 × 4 inductive pressure sensor array into a wearable keyboard for a smart electronic calendar application.

ANTERIOR CRUCIATE LIGAMENT SECTIONING ALTERS CENTER OF PRESSURE WITHIN THE TIBIOFEMORAL JOINT: AN IN VITRO STUDY

Anterior cruciate ligament (ACL) injuries often lead to secondary injuries, joint degradation, and were linked to osteoarthritis. There is little known about how ACL rupture affects the loading and contact characteristics within the tibiofemoral joint. The objective of this study was to evaluate changes in tibiofemoral joint contact pressure and center of pressure (COP) during dynamic motion before and after ACL sectioning in vitro. Six intact cadaveric knees were manipulated through three full cycles of motion ranging from 30∘ to 120∘ of flexion in a custom-built device. A pressure sensor inserted in the tibiofemoral joint measured contact pressure of the medial and lateral compartments as well as COP characteristics of the whole joint before and after the ACL was sectioned. There was a significant decrease in lateral-compartment peak pressure, medial and lateral mean pressure, and total contact area after the ACL was sectioned. In both intact and ACL deficient knees, a posterior-lateral shift in COP was observed during flexion and a medial-anterior shift when returning to extension. Plotting the COP trajectory through the flexion-extension cycle resulted in a distinct hysteresis curve due to the viscoelastic soft tissue properties. Following sectioning, the COP trajectory had a diminished area compared to the intact condition. The diminished area of contact pressure may be more problematic than the overall magnitude when the integrity of the ACL is compromised. The centralized pressure distribution to a smaller surface area over time may cause focal damage to the cartilage leading to osteoarthritis.

The relationships of gripping comfort to contact pressure and hand posture during gripping

A sensory evaluation test on spherical and columnar objects with different cross-sectional shapes was conducted to investigate their gripping comfort. The relationships of the gripping comfort with the measured contact pressure and hand posture during each grasping task were then statistically analysed using regression analysis with a stepwise procedure. The coefficient of determination of the correlation between the contact-pressure distribution and gripping comfort indicated a fairly strong correlation (R2 = 0.55), which is stronger than the correlation between the finger joint angles and gripping comfort (R2 = 0.33). The cross-sectional shapes of the test objects caused variations in the contact-pressure distribution owing to changes of the contacting part and the grasping strategy. Furthermore, the contact pressures on the fingertips, the distal region of the palm close to the index finger, and the proximal region on the palm close to the radius all contributed to the gripping comfort, according to the analysis results. The result allows a better understanding of the performance of contact pressure and hand posture in evaluating gripping comfort as well as the role of local contact pressures in the prediction of gripping comfort. Manufacturers can select the local contact pressures that strongly contribute to the gripping comfort during the assessment of their products.

Optical Fibre-Based Pulse Oximetry Sensor with Contact Force Detection.

A novel optical sensor probe combining monitoring of blood oxygen saturation (SpO2) with contact pressure is presented. This is beneficial as contact pressure is known to affect SpO2 measurement. The sensor consists of three plastic optical fibres (POF) used to deliver and collect light for pulse oximetry, and a fibre Bragg grating (FBG) sensor to measure contact pressure. All optical fibres are housed in a biocompatible epoxy patch which serves two purposes: (i) to reduce motion artefacts in the photoplethysmogram (PPG), and (ii) to transduce transverse loading into an axial strain in the FBG. Test results show that using a combination of pressure measuring FBG with a reference FBG, reliable results are possible with low hysteresis which are relatively immune to the effects of temperature. The sensor is used to measure the SpO2 of ten volunteers under different contact pressures with perfusion and skewness indices applied to assess the quality of the PPG. The study revealed that the contact force ranging from 5 to 15 kPa provides errors of <2%. The combined probe has the potential to improve the reliability of reflectance oximeters. In particular, in wearable technology, the probe should find use in optimising the fitting of garments incorporating this technology.

Pilot Biomechanical Evaluation of Spring Ligament Augmentation with the Internal Brace in a Cadaveric Flatfoot Model

Category: Hindfoot Introduction/Purpose: Surgical reconstruction for flexible acquired flatfoot deformity from posterior tibial tendon dysfunction has been described and often includes a medial displacing calcaneal osteotomy (MDCO), Flexor digitorum longus (FDL) transfer, and possible spring ligament repair. However, the spring ligament is often attenuated leaving surgeons with few options for robust repair. Meanwhile, the Internal Brace (Arthrex, Naples, Florida) has been reported in a patient series as an excellent adjunct for spring ligament augmentation for the treatment of flatfoot correction with good clinical results. However, there are no biomechanical studies, which evaluate its safety or efficacy. The aim of this study is to perform a biomechanical comparison of spring ligament repair with Internal Brace augmentation to controls undergoing reconstruction of a flatfoot model. Methods: 4 paired (8 total), below the knee, cadaveric specimens, age 45.3 years (range; 30-60), without pre-existing foot deformity were utilized. Flatfoot model was achieved as described in the literature. Surgical reconstruction included MDCO (7.5 mm calcaneal plate), a spring ligament repair reefing (2-0 fiber wire suture), and an FDL transfer through a navicular bone tunnel with interference fixation via a biotenodesis screw (Arthrex, Naples, Florida). The experimental group received spring ligament augmentation with an internal brace as described by the manufacturer’s specifications. After potting, specimens were loaded statically to measure contact pressures and flatfoot correction. Achilles was tensioned to 350 N and cyclic loading was performed in a stepwise fashion after preconditioning. Loading occurred at 1 Hertz for 100 cycles, increasing at 100 N intervals to 1800 N. Tekscan contact pressures, radiography, and digitized measurements were repeated. Spring ligament repair site was evaluated and failures were recorded. Results: There was a statistically significant difference under cyclic loading of the internal brace augmented repair compared to standard suture repair alone (p=0.001). There were no failures of the internal brace device. Control spring ligament repair failed via suture cutout. There was 1 catastrophic specimen failure through the tibio-talar joint in each group (1000 N control; 1800 N experimental). The average change in talometatarsal angle was not statistically significant between the control (4.31±2.82) and the internal brace (4.06±2.74) (p=0.66) after loading. There was no difference in the change of peak intra-articular contact pressure at the talonavicular joint between flatfoot model and surgical correction when comparing the internal brace reconstruction (1478.8±306.6 pKa) and controls (1816.5 ±436.7pKa) (p=0.79). Conclusion: The use of the Internal Brace device to augment spring ligament reefing repair appears biomechanically safe and effective under cyclic specimen loading in a pilot, cadaveric flatfoot reconstruction model. Furthermore, it does not appear to alter intra-articular talonavicular joint contact pressures.

Effective Stress Strength Parameters of Clays from DMT

Abstract In this study, an established effective stress limit plasticity solution for piezocone penetration tests (CPTu) in clay developed by the Norwegian Institute of Technology (NTH) for evaluating the effective stress friction angle (ϕ′) is extended to flat plate dilatometer tests (DMT) readings. A nexus between CPTu and DMT is built through spherical cavity expansion solutions for undrained penetration to link the cone tip resistance (qt) and shoulder porewater pressure (u2) from CPTu to the measured contact pressure (p0) and expansion pressure (p1) obtained from DMT in soft to firm intact clays. Data from 49 paired sets of CPTu-DMT soundings in a variety of clays are used to support and validate the links. A variety of soils ranging from lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins are subjected to flat DMTs, and the measurements are utilized to evaluate the effective stress friction angle (ϕ′). Data from 46 clays are compiled to examine the DMT-interpreted ϕ′ values in comparison with laboratory benchmark ϕ′ values obtained from CAUC or isotropically consolidated undrained triaxial compression tests on high-quality samples. An approximate inversion of the theoretical solution is derived to allow ϕ′ profiles to be determined with depth. Four well-documented DMT examples, including two natural clay sites and two chamber test series (one pressurized and the other unpressurized), are presented to illustrate the NTH procedures.

Three Dimensional Distribution of Sensitive Field and Stress Field Inversion of Force Sensitive Materials under Constant Current Excitation.

Force sensitive conductive composite materials are functional materials which can be used as the sensitive material of force sensors. However, the existing sensors only use one-dimensional electrical properties of force sensitive conductive materials. Even in tactile sensors, the measurement of contact pressure is achieved by large-scale arrays and the units of a large-scale array are also based on the one-dimensional electrical properties of force sensitive materials. The main contribution of this work is to study the three-dimensional electrical properties and the inversion method of three-dimensional stress field of a force sensitive material (conductive rubber), which pushes the application of force sensitive material from one dimensional to three-dimensional. First, the mathematical model of the conductive rubber current field distribution under a constant force is established by the effective medium theory, and the current field distribution model of conductive rubber with different geometry, conductive rubber content and conductive rubber relaxation parameters is deduced. Secondly, the inversion method of the three-dimensional stress field of conductive rubber is established, which provides a theoretical basis for the design of a new tactile sensor, three-dimensional stress field and space force based on force sensitive materials.

Customized design and 3D printing of face seal for an N95 filtering facepiece respirator

ABSTRACTFiltering Facepiece Respirator (FFR) is the most common respirator users in the health care environment utilize for personal protection from outside particles. Comfort and fit are important while wearing an FFR. This paper proposes a novel technology to produce customized face seal design for improving the wearing comfort and fit of FFR wearers. In order to customize the design of face seals, we scanned the faces of three subjects using three-dimensional (3D) laser scanning method. A customized face seal for a 3M 8210 N95 FFR for each headform was designed using reverse engineering technique. Next, the face seal prototypes were fabricated with Acrylonitrile Butadiene Styrene (ABS) plastic using the 3D printing method. A force sensing system based on Arduino Uno R3 was developed, and the force sensor of this system was inserted between the FFR and headform to measure contact pressure. Experimental results showed that the newly designed FFR face seal provided the subjects with an improved contact pressure.

A new system for the measurement of gripping force based on scattering

&lt;p style="margin: 0cm 0cm 0pt;"&gt;&lt;span lang="EN-US"&gt;&lt;span style="font-family: Calibri; font-size: small;"&gt;The measurement of contact pressure of human fingers is very important to understand human perceptual mechanisms, that is the main goal of most of the neuroscientific studies. It may also lead to a correct development of tactile devices and haptic systems, as they are intended to convey controllable and effective stimuli.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;&lt;span style="font-family: 'Garamond','serif'; font-size: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-GB; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-GB"&gt;In this work, an optical measurement system based on Frustrated Total Internal Reflection (FTIR) is proposed for the measurement of the pressure distribution on the contact area between a human finger and a flat surface. The feasibility study performed shows that the tested sensor can be effectively used for the measurement of the fingertip contact pressure both on static and dynamic conditions.&lt;/span&gt;

Influence of the Contact Area on the Current Density across Molecular Tunneling Junctions Measured with EGaIn Top-Electrodes

This paper describes the relationship between the rates of charge transport (by tunneling) across self-assembled monolayers (SAMs) in a metal/SAM//Ga2O3/EGaIn junction and the geometric contact area (Ag) between the conical Ga2O3/EGaIn top-electrode and the bottom-electrode. Measurements of current density, J(V), across SAMs of decanethiolate on silver demonstrate that J(V) increases with Ag when the contact area is small (Ag < 1000 μm2), but reaches a plateau between 1000 and 4000 μm2, where J(0.5 V) ≈ 10–0.52±0.10 A/cm2. The method used to fabricate Ga2O3/EGaIn electrodes generates a tip whose apex is thicker and rougher than its thin, smoother sides. When Ag is small, the Ga2O3/EGaIn electrode contacts the bottom-electrode principally over this rough apex and forms irreproducible areas of electrical contact. When Ag is large, the contact is through the smoother regions peripheral to the apex and is much more reproducible. Measurements of contact pressure between conical EGaIn electrodes and atomic forc...

Assessment of an active industrial exoskeleton to aid dynamic lifting and lowering manual handling tasks

The aim of this study was to evaluate the effect of an industrial exoskeleton on muscle activity, perceived musculoskeletal effort, measured and perceived contact pressure at the trunk, thighs and shoulders, and subjective usability for simple sagittal plane lifting and lowering conditions. Twelve male participants lifted and lowered a box of 7.5 kg and 15 kg, respectively, from mid-shin height to waist height, five times, both with and without the exoskeleton. The device significantly reduced muscle activity of the Erector Spinae (12%-15%) and Biceps Femoris (5%). Ratings of perceived musculoskeletal effort in the trunk region were significantly less with the device (9.5%-11.4%). The measured contact pressure was highest on the trunk (91.7 kPa-93.8 kPa) and least on shoulders (47.6 kPa-51.7 kPa), whereas pressure was perceived highest on the thighs (35-44% of Max LPP). Six of the users rated the device usability as acceptable. The exoskeleton reduced musculoskeletal loading on the lower back and assisted with hip extensor torque during lifting and lowering. Contact pressures fell below the Pain Pressure Threshold. Perceived pressure was not exceptionally high, but sufficiently high to cause discomfort if used for long durations.

Development of thin and flexible contact pressure sensing system for high spatial resolution measurements

Evaluations of stress applied conditions are important for a diagnosis of human joint diseases. Measuring contact pressure distributions at the interface area of small joints such as finger joint surfaces is difficult due to the spatial limitation of sensors. Two contact pressure sensor units have high spatial resolution of 90μm with 24×24 and 128×128 measurement points were developed in this study. The system accuracy was quantitatively confirmed by measuring the pressure distribution pattern during a cylindrical-shaped punch impressed on the sensor. The measured pressure distribution agreed well with the theoretical compression pattern. The contacting area was recognized as 110% of the actual cross-sectional area of punch, and the total force value calculated from the integration of pressure distributed over the contacting area was 93% of the applied force. Moreover, a complex pattern of coin surface was obtained as the pressure distributions in this sensing system. As an application, the sensor was inserted to a small joint part in chicken wing for pressure measurements at the interface. The possibility of measuring the dynamic change of pressure distribution at narrow joint space was shown in this study.

Development of a conformable electronic skin based on silver nanowires and PDMS

This paper presented the designed and tested a flexible and stretchable pressure sensor array that could be used to cover 3D surface to measure contact pressure. The sensor array is laminated into a thin film with 1 mm in thickness and can easily be stretched without losing its functionality. The fabricated sensor array contained 8×8 sensing elements, each could measure the pressure up to 180 kPa. An improved sandwich structure is used to build the sensor array. The upper and lower layers were PDMS thin films embedded with conductor strips formed by PDMS-based silver nanowires (AgNWs) networks covered with nano-scale thin metal film. The middle layer was formed a porous PDMS film inserted with circular conductive rubber. The sensor array could detect the contact pressure within 30% stretching rate. In this paper, the performance of the pressure sensor array was systematically studied. With the corresponding scanning power-supply circuit and data acquisition system, it is demonstrated that the system can successfully capture the tactile images induced by objects of different shapes. Such sensor system could be applied on complex surfaces in robots or medical devices for contact pressure detection and feedback.

Spherically capped membrane probes for low contact pressure tribology

Low contact pressure measurements are needed for biotribology studies on cells, cell layers, and tissues. Such studies typically require low forces to achieve kPa range contact pressures, but such methods frequently come at the expense of contact area and, in turn, relevance. In seeking lower contact pressures, the corresponding contact areas can become too small to be physiologically relevant or important. The recently developed method creates probes that are thin spherical shells, specifically designed to create low contact pressures. These polyethylene glycol and polyacrylamide hydrogel probes were polymerized with embedded fluorescent nanoparticles, and indentation experiments were performed in situ on a confocal microscope to determine the deformation mechanics. The indentation load versus contact width behavior revealed that this design has the ability to achieve pressures in the kPa range at macroscopic contact areas that are independent of the applied load (i.e., the area grows linearly with the applied load, leading to a constant contact pressure).

Measurement of Hip Contact Pressure During Arthroscopic Femoroacetabular Impingement Surgery

Cam impingement is caused by jamming of an abnormal femoral head with an increased radius into the acetabulum during motion. Therefore, the elevation of the contact pressure during the motion is suspected to be an essential pathology of femoroacetabular impingement. However, there is no method to quantify the hip contact pressure during motion. The purpose of this Technical Note is to introduce a technique to measure the hip contact pressure during arthroscopic surgery. The author believes that the current technique will be a useful tool for the detailed investigation of the pathophysiology femoroacetabular impingement and thorough evaluation of its therapeutic significance.

Design of a Wireless Medical Capsule for Measuring the Contact Pressure Between a Capsule and the Small Intestine.

A wireless medical capsule for measuring the contact pressure between a mobile capsule and the small intestine lumen was developed. Two pressure sensors were used to measure and differentiate the contact pressure and the small intestine intraluminal pressure. After in vitro tests of the capsule, it was surgically placed and tested in the proximal small intestine of a pig model. The capsule successfully gathered and transmitted the pressure data to a receiver outside the body. The measured pressure signals in the animal test were analyzed in the time and frequency domains, and a mathematic model was presented to describe the different factors influencing the contact pressure. A novel signal processing method was applied to isolate the contraction information from the contact pressure. The result shows that the measured contact pressure was 1.08 ± 0.08 kPa, and the small intestine contraction pressure's amplitude and rate were 0.29 ± 0.046 kPa and 12 min-1. Moreover, the amplitudes and rates of pressure from respiration and heartbeat were also estimated. The successful preliminary evaluation of this capsule implies that it could be used in further systematic investigation of small intestine contact pressure on a mobile capsule-shaped bolus.

Test and fabrication of piezoresistive sensors for contact pressure measurement

The use of contact pressure sensors has become popular in various engineering disciplines in recent years. They are used in characterization of vehicle tires, bearings, wind tunnels, prosthesis design, ergonomic analysis among other areas. These sensors are fabricated with materials that have certain properties such as piezoelectricity, piezoresistance and variable capacitance; however, the most used characteristic is the piezoresistive effect. This paper describes the fabrication of three different sensors using piezoresistive materials. Furthermore, a comparative technical study including a commercial sensor as a benchmark is done with the aim of selecting a suitable material when measuring contact pressure. The repeatability and hysteresis of each sensor were evaluated in a response to load test realized several times. A time drift test with a dead load was also performed for evaluating stability. Finally, some recommendations are given regarding the type of material to be used in pressure sensors for engineering applications, particularly in the biomedical field

Low-Cost Disposable Tactile Sensors for Palpation in Minimally Invasive Surgery

Robot-assisted minimally invasive surgery prevents surgeons from manually palpating organs to locate subsurface tumors and other structures. One solution is to use ultrasound; however, it is not always reliable. Tactile sensor arrays have been proposed as an alternative or complementary modality, but current designs have drawbacks including a large number of wires, lack of autoclavability or disposability and high cost. In this paper, four mass-producible, low-cost, sterilizable tactile sensor array designs with minimal wires are presented. Both piezoresistive and capacitive versions have been designed, each with a 2 mm $\times$ 2 mm spatial resolution and a scan rate of 30 Hz. Two sizes with 48 or 90 sensing elements are presented for each version. The sensing elements can measure contact pressures with 1 kPa resolution and they have over 84% accuracy in the 25–150 kPa range. The low cost allows the sensors to be made disposable, avoiding the deterioration in performance resulting from repeated autoclaving. The sensors include the analog-to-digital conversion circuit onboard, requiring only two power lines and two digital signal lines to connect them. The small number of output wires allows the sensors to be incorporated into robotic surgical instruments with articulated wrists that do not have the space for a large number of wires. Both sensor versions are shown to be able to detect 6-mm-diameter tumors at a depth of 10 mm in a silicone phantom and in ex vivo tissue samples.

Finite Element Digital Human Hand Model-Case Study of Grasping a Cylindrical Handle

Products are becoming increasingly complex, therefore designers are faced with a challenging task to incorporate new or improved functionality, higher performance and optimal shape design. Traditional user-centered design techniques such as designing with anthropometric data do not incorporate enough user data to design better products for the target population. Measurements of contact pressure and contact area using traditional methods are time consuming and require actual product prototype and expensive measurement systems. In order to overcome these limitations, several researchers already proposed the use of computer simulations using finite element (FE) method. Therefore the aim of this research was to develop an anatomically accurate and numerically feasible and stable finite element digital human hand model with bio-mechanically accurate hand movement and grasping, which would allow virtual analyses of stresses on the soft tissue. The usability of the developed model is presented on a case study grasping a cylindrical handle.