Finger Path Research Articles

Experimental and simulation analysis of liquid capillary fingering process in the gas diffusion layer

In a proton exchange membrane fuel cell (PEMFC), water movement through the gas diffusion layer (GDL) is essential for water management. Using a combination of experiments and simulations, this paper investigates the capillary fingering process of liquid water within the GDL and analyzes the effects of flow field type, GDL compression ratio, and contact angle on the capillary fingering of liquid water within the GDL. The results reveal finger-stopping, splitting, and fusion during the injection of non-wetting liquid, which is not conducive to rapid water movement within the GDL. When water breaks through the top layer of the fibers, a finger path between the inlet and the gas channel is formed, and the liquid preferentially migrates along this path. Due to the existence of air cross-flow, the GDL water saturation for the serpentine/cross-finger flow field is 17.2%. The water preferentially produces directional flow in the through-plane direction as the compression ratio rises, and the GDL water saturation falls to 24.18%. The distribution of anisotropic contact angles determines the flow state of liquid water, making water removal from the GDL easier. The results and findings here are expected to lead to more reliable water management and related high-power technologies of PEMFCs.

Design of a flexible bio-inspired stretch-forming machine for the fabrication of large radius bends parts

The imitation and application of manipulability and dexterity of human arm have been investigated actively as it can improve the time efficiency and save labor cost greatly. Most of the current studies in this area only focus on recreating the structure of human arm without considering how to use the finger path for forming. In this paper, the authors present a flexible bio-inspired stretch-forming machine (SFM) for the fabrication of parts, which are large and possess large radius bends, with small spring back and smooth surfaces. The flexible bio-inspired SFM was composed by two pairs of finger-inspired jaws in conjunction with six couples of muscle-inspired hydraulic cylinders (the sum of numbers is 60), which only integrates six solenoid types of reversing valves. The path of finger-inspired jaws was planned by setting up the parameters of loading order, stretching direction, and cylinder pull force. The finger-inspired jaws, driven by the muscle-inspired hydraulic cylinders, moved along the given route to realize sheet metal forming. The finite element simulation and experiment results on a series of large radius bends parts formed by the flexible finger-inspired SFM have been reported. The remarkable results are that an effective solution for stretch forming of sheet metal with short free edge has been founded, and an easy control process of stretch forming with finger-inspired jaws has been developed, respectively. This work has an important value in implementation of stretch-forming technology from aircraft to vehicle and building.

Nondestructive three-dimensional observations of flow finger and lateral flow development in dry snow using magnetic resonance imaging

Flow fingers develop due to the infiltration of snow meltwater or rain water into a dry snowpack. The width, spacing, and areal coverage of the flow finger path and occurrence of capillary barriers have been demonstrated using dye tracer experiments that were conducted in the field and in cold laboratories. Because dye tracer experiments require the destructive analysis of the snow, the initial shape, and the temporal development of fingering and lateral flows are unclear. To examine this, we carried out nondestructive observations of flow finger development, and the formation of capillary barriers using two different dry snow samples in a cold laboratory using magnetic resonance imaging (MRI) with a three-dimensional rapid imaging method. X-ray micro-computed tomography (μCT) was also used to determine the relationship between the water flow phenomena and the snow microstructure. The experimental results showed that flow fingers developed in dry snow samples. The number of flow finger paths increased, and a lateral flow developed through the continuing water supply. The small discontinuity of the pore size and snow density in the vertical direction acted as a capillary barrier and induced lateral flow. These results showed that both the persistence of the flow finger path and the increase in the number of flow paths are important for understanding the infiltration of water into dry snow and for developing a snowpack model that includes water-moving processes. Nondestructive observation using MRI is a promising technique to follow the development of preferential flow path and lateral flow. Detailed information regarding the heterogeneity of the pore distribution and snow microstructures in a layered snowpack is required to understand the water flow phenomena in a natural snowpack.

Fine line screen printed silver electrodes for copper electrodeposition

Purpose In this paper, results of the studies on the copper deposition on screen-printed fine-line front electrode of the solar cell were presented. The silver consumption is an important problem according to growing silver prices. The proposed solution of those problems might be printing of a very thin silver seed layer and subsequent copper plating. This process can be an alternative for typically used screen printing. The purpose of this study was the optimization of the finger path fabrication process to obtain required geometric of fingers for copper deposition. Design/methodology/approach In this paper, double-step metallization process was analyzed. The first step of an electrode formation is screen printing, the second one is copper electrodeposition. Presented investigations were focused on the optimization of the finger path fabrication process to obtain required geometric dimensions and sharp border of fingers. The morphology of the electrodes was characterized by scanning electron microscope before and after copper deposition. The X-ray analysis of elemental arrangement and cross-section profiles of fingers were made using energy-dispersive X-ray fluorescence spectrometer. Findings Presented investigations were focused on the optimization of the finger path fabrication process to obtain required geometric dimensions and sharp border of fingers without any silver particles. The main problem of non-uniform silver paste distribution close to the border of printed finger paths was eliminated by selection of appropriate paste and printing parameters. The obtained coatings were soft, ductile and bright. Originality/value The novelty of the presented approach is modification of the printing parameters, especially for copper deposition. In this paper, the reasons of the widening of electrodes during the copper deposition process is analyzed.

Evaluating touch-screen vibration modality for blind users to access simple shapes and graphics

Accessing visual information becomes a central need for all kinds of tasks and users (from accessing graphics and charts in news articles, to viewing images of items on sale on e-commerce sites), especially for blind users. In this context, digital tools of assistance, using adapted software (screen readers, talking browsers, etc.), hardware (force feedback mouse, piezo-electric pins, etc.), and more recently touch-screen technology (using smart phones or smart tablets) have been increasingly helping blind persons access and manipulate information. While effective with textual information, yet existing solutions remain limited when handling visual information. In this context, the goal of our study is to shed light on how the vibration modality can be perceived by blind users when accessing simple contour-based images and visual graphics on a touch-screen. In this paper, we target the vibration-only modality, compared with audio-kinesthetic or multimodal vibro-audio solutions. Our main motivation is that the potentials and limitations of touch-screen vibration-only feedback need to be fully studied and understood prior to integrating other modalities (such as sound, human speech, or other forms of haptic feedback). This could prove very useful in a range of applications: allowing blind people to access geographic maps, to navigate autonomously inside and outside buildings, as well as to access graphs and mathematical charts (for blind students). To achieve our goal, we develop a dedicated experimental protocol, titled EVIAC, testing a blind user's capacity in learning, distinguishing, identifying, and recognizing basic shapes and geometric objects presented on a vibrating touch-screen. Extensive tests were conducted on blindfolded and blind candidates, using a battery of evaluation metrics including: i) accuracy of shape recognition, ii) testers average response time, iii) number and duration of finger strokes, iv) surface area covered by the testers finger path trails, as well as iv) finger path correlation with the surface of the target shape. Results show that blind users are generally capable of accessing simple shapes and graphics presented on a vibrating touch-screen. However, results also underline various issues, ranging over: prolonged response time (e.g., blind users require 1min and 22s on average to recognize a basic shape), reduced touch-screen surface coverage, and low correlation between the surface of the target shape and the tester's vibration trails. The latter issues need to be further investigated to produce optimal recipes for using touch-screen technology to support image accessibility for blind users.

Copper deposition on screen printed electrical paths for solar cell application

Purpose – The aim of this paper is to present results of investigations carried out on the front electrode of solar cells. Nowadays, most worldwide solar cell production is dominated by monocrystalline and polycrystalline silicon as a base material. In such cells, the electrical carriers are collected by the system of metallic paths fabricated on a silicon surface. One possible way to increase cell efficiency and reduce the production costs of solar modules is to replace the expensive silver by cheaper copper in front metallic electrodes. Design/methodology/approach – The paper presents results of investigations performed on the front electrode of the solar cell. The investigations were focused on the modification of typical screen printing fabrication of the thin electrical finger paths of the front solar cell electrode. The resulting contacts were characterized morphologically (the dimensions and geometry of the front contacts) by scanning electron microscopy. The composition of finger path covered with copper was analyzed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques. Findings – In this work, the front electrodes were screen printed with the use of conventional silver-paste on a p-type Cz–Si-textured wafer with a n+ emitter and with an antireflection coating. After that, the fired front electrode was electroless coated with copper. The electroless copper deposition was performed in two stages. First, the surface of the photovoltaic cell was dipped in an aqueous solution of CuSO4 and then dried in air at room temperature. When the surface dried, the cell was immersed in hydrogen fluoride solution (5 per cent) for 1 s followed by rinsing in deionization water. Originality/value – The experiments confirmed the potential application of copper as an additional layer of the solar cell front metal electrode. On the one hand, this process is very simple and, on the other, the authors demonstrate a problem with the mechanical stability of the covered paths leading to electrode delamination.

Following and intercepting scribbles: interactions between eye and hand control

The smooth pursuit eye movement system appears to be importantly engaged during the planning and execution of interceptive hand movements. The present study sought to probe the interaction between eye and hand control systems by examining their responses during an interception task that included target speed perturbations. On 2/3 of trials, the target increased or decreased speed at various times, ranging from about 300ms before to 150ms after the onset of a finger movement directed to intercept the target and was triggered by a GO signal. Additionally, the same 2D sum-of-sines target trajectories were followed with the eyes without interception. The smooth pursuit system responded more quickly if the target speed perturbation occurred earlier during the reaction time (i.e., near the time of the GO signal). Similarly, the finger movement began more quickly if target speed was increased earlier during the reaction time. For early perturbation conditions, the initial direction of the finger movement matched the predicted target intercept using the new target speed. For perturbations occurring after finger movement, onset initial direction of finger movement did not match target interception such that the finger path began to curve toward the perturbed target after about 150-200ms. The results support the idea of an active process of visual target path extrapolation simultaneously used to guide both the eye and hand.

Getting a grip: different actions and visual guidance of the thumb and finger in precision grasping

We manipulated the visual information available for grasping to examine what is visually guided when subjects get a precision grip on a common class of object (upright cylinders). In Experiment 1, objects (2 sizes) were placed at different eccentricities to vary the relative proximity to the participant's (n=6) body of their thumb and finger contact positions in the final grip orientations, with vision available throughout or only for movement programming. Thumb trajectories were straighter and less variable than finger paths, and the thumb normally made initial contact with the objects at a relatively invariant landing site, but consistent thumb first-contacts were disrupted without visual guidance. Finger deviations were more affected by the object's properties and increased when vision was unavailable after movement onset. In Experiment 2, participants (n=12) grasped 'glow-in-the-dark' objects wearing different luminous gloves in which the whole hand was visible or the thumb or the index finger was selectively occluded. Grip closure times were prolonged and thumb first-contacts disrupted when subjects could not see their thumb, whereas occluding the finger resulted in wider grips at contact because this digit remained distant from the object. Results were together consistent with visual feedback guiding the thumb in the period just prior to contacting the object, with the finger more involved in opening the grip and avoiding collision with the opposite contact surface. As people can overtly fixate only one object contact point at a time, we suggest that selecting one digit for online guidance represents an optimal strategy for initial grip placement. Other grasping tasks, in which the finger appears to be used for this purpose, are discussed.

A real-time strategy for dexterous manipulation: Fingertips motion planning, force sensing and grasp stability

This paper presents a global strategy for object manipulation with the fingertips with an anthropomorphic dexterous hand: the LMS Hand of the ROBIOSS team from PPRIME Institute in Poitiers (France). Fine manipulation with the fingertips requires to compute on one hand, finger motions able to produce the desired object motion and on the other hand, it is necessary to ensure object stability with a real time scheme for the fingertip force computation. In the literature, lot of works propose to solve the stability problem, but most of these works are grasp oriented; it means that the use of the proposed methods are not easy to implement for online computation while the grasped object is moving inside the hand. Also simple real time schemes and experimental results with full-actuated mechanical hands using three fingers were not proposed or are extremely rare. Thus we wish to propose in a same strategy, a robust and simple way to solve the fingertip path planning and the fingertip force computation. First, finger path planning is based on a geometric approach, and on a contact modelling between the grasped object and the finger. And as force sensing is required for force control, a new original approach based on neural networks and on the use of tendon-driven joints is also used to evaluate the normal force acting on the finger distal phalanx. And an efficient algorithm that computes fingertip forces involved is presented in the case of three dimensional object grasps. Based on previous works, those forces are computed by using a robust optimization scheme. In order to validate this strategy, different grasps and different manipulation tasks are presented and detailed with a simulation software, SMAR, developed by the PPRIME Institute. And finally experimental results with the real hand illustrate the efficiency of the whole approach.

Modular Control of Pointing beyond Arm's Length

Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant kinematic chain allowing simultaneous target reaching and regulation of the center of mass (CoM) displacement in extrinsic space emerged from the first analysis. In follow-up experiments, both the CoM and finger trajectories were constrained by asking participants to reach from a reduced base of support with or without knee flexion, or by moving the endpoint along a predefined trajectory (straight or semicircular trajectories). Whereas joint covaried during free conditions and under equilibrium restrictions, it was decomposed in two task-dependent and task-independent modules, corresponding to a dissociation of arm versus legs, trunk, and head coordination, respectively, under imposed finger path conditions. A numerical simulation supported the idea that both postural and focal subtasks are basically integrated into the same motor command and that the CNS is able to combine or to separate the movement into autonomous functional synergies according to the task requirements.

Novel muscle patterns for reaching after cervical spinal cord injury: a case for motor redundancy

A fundamental issue in the neuromotor control of arm movements is whether the nervous system can use distinctly different muscle activity patterns to obtain similar kinematic outcomes. Although computer simulations have demonstrated several possible mechanical and torque solutions, there is little empirical evidence that the nervous system actually employs fundamentally different muscle patterns for the same movement, such as activating a muscle one time and not the next, or switching from a flexor to an extensor. Under typical conditions, subjects choose the same muscles for any given movement, which suggests that in order to see the capacity of the nervous system to make a different choice of muscles, the nervous system must be pushed beyond the normal circumstances. The purpose of this study, then, was to examine an atypical condition, reaching of cervical spinal cord injured (SCI) subjects who have a reduced repertoire of available distal arm muscles but otherwise a normal nervous system above the level of lesion. Electromyography and kinematics of the shoulder and elbow were examined in the SCI subjects performing a center-out task and then compared to neurologically normal control subjects. The findings showed that the SCI-injured subjects produced reaches with typical global kinematic features, such as straight finger paths, bell-shaped velocities, and joint excursions similar to control subjects. The SCI subjects, however, activated only the shoulder agonist muscle for all directions, unlike the control pattern that involved a reciprocal pattern at each joint (shoulder, elbow, and wrist). Nonetheless, the SCI subjects could activate their shoulder antagonist muscles, elbow flexors, and wrist extensor (extensor carpi radialis) for isometric tasks, but did not activate them during the reaching movements. These results demonstrate that for reaching movements, the SCI subjects used a strikingly different pattern of intact muscle activities than control subjects. Hence, the findings imply that the nervous system is capable of choosing either the control pattern or the SCI pattern. We would speculate that control subjects do not select the SCI pattern because the different choice of muscles results in kinematic features (reduced fingertip speed, multiple shoulder accelerations) other than the global features that are somehow less advantageous or efficient.

Unstable Flow during Redistribution in Homogeneous Soil

Two‐ and three‐dimensional laboratory experiments were conducted in a large 1 by 1 m2 Hele–Shaw cell and a 10‐cm cylinder column to study the stability of the redistribution process in a uniformly packed porous medium of coarse sand. Our results demonstrate that fingers form and propagate rapidly as soon as infiltration stops when the soil is initially dry, but form more slowly and are larger when the soil is wet. Finger widths ranged from about 4.5 cm when the soil was dry to 17 cm when the soil was very wet, and the fraction of the cross‐sectional area occupied by fingers also increased (from 36 to 66%). Finger velocities declined with time in all studies, with averages ranging from 3.6 to 9.6 cm min−1. We demonstrated that ponded infiltration was stable and uniform in our system, so that the fingering we observed was not due to soil heterogeneity. The porous medium retained a memory of the fingers formed in the first experiment, so fingers formed in subsequent redistribution cycles followed the old finger paths, even after 28 d had elapsed. Fingers provide channels for rapid drainage of previously infiltrated water, especially when the soil ahead of the front is dry. Our findings clearly contradict predictions made by the Richards equation, which calculates stable flow during redistribution in homogeneous soil.

Unstable Flow during Redistribution in Homogeneous Soil

Two- and three-dimensional laboratory experiments were conducted in a large 1 by 1 m 2 Hele–Shaw cell and a 10-cm cylinder column to study the stability of the redistribution process in a uniformly packed porous medium of coarse sand. Our results demonstrate that fingers form and propagate rapidly as soon as infiltration stops when the soil is initially dry, but form more slowly and are larger when the soil is wet. Finger widths ranged from about 4.5 cm when the soil was dry to 17 cm when the soil was very wet, and the fraction of the cross-sectional area occupied by fingers also increased (from 36 to 66%). Finger velocities declined with time in all studies, with averages ranging from 3.6 to 9.6 cm min −1 . We demonstrated that ponded infiltration was stable and uniform in our system, so that the fingering we observed was not due to soil heterogeneity. The porous medium retained a memory of the fingers formed in the first experiment, so fingers formed in subsequent redistribution cycles followed the old finger paths, even after 28 d had elapsed. Fingers provide channels for rapid drainage of previously infiltrated water, especially when the soil ahead of the front is dry. Our findings clearly contradict predictions made by the Richards equation, which calculates stable flow during redistribution in homogeneous soil.

General coordination of shoulder, elbow and wrist dynamics during multijoint arm movements.

Studies of multijoint arm movements have demonstrated that the nervous system anticipates and plans for the mechanical effects that arise from motion of the linked limb segments. The general rules by which the nervous system selects appropriate muscle activities and torques to best deal with these intersegmental effects are largely unknown. In order to reveal possible rules, this study examined the relationship of muscle and interaction torques to joint acceleration at the shoulder, elbow and wrist during point-to-point arm movements to a range of targets in the horizontal plane. Results showed that, in general, dynamics differed between the joints. For most movements, shoulder muscle torque primarily determined net torque and joint acceleration, while interaction torque was minimal. In contrast, elbow and wrist net torque were determined by a combination of muscle and interaction torque that varied systematically with target direction and joint excursion. This "shoulder-centered pattern" occurred whether subjects reached targets using straight or curved finger paths. The prevalence of a shoulder-centered pattern extends findings from a range of arm movement studies including movement of healthy adults, neurological patients, and simulations with altered interaction effects. The shoulder-centered pattern occurred for most but not all movements. The majority of the remaining movements displayed an "elbow-centered pattern," in which muscle torque determined initial acceleration at the elbow and not at the shoulder. This occurred for movements when shoulder excursion was <50% of elbow excursion. Thus, both shoulder- and elbow-centered movements displayed a difference between joints but with reversed dynamics. Overall, these findings suggest that a difference in dynamics between joints is a general feature of horizontal plane arm movements, and this difference is most commonly reflected in a shoulder-centered pattern. This feature fits well with other general shoulder-elbow differences suggested in the literature on arm movements, namely that: (a) agonist muscle activity appears more closely related to certain joint kinematics at the shoulder than at the elbow, (b) adults with neurological damage display less disruption of shoulder motion than elbow motion, and (c) infants display adult-like motion first in the shoulder and last at the wrist.

Tactile input of the hand and the control of reaching to grasp movements

The role of tactile information of the hand in the control of reaching to grasp movements was investigated. The kinematics of both reaching (or transport) and grasp components were studied in healthy subjects in two experimental conditions. In one condition (control condition) subjects were required to reach and grasp an object that could have two sizes and that could be located at two distances from the viewer. In the other condition (anaesthesia condition) the same movements were executed, but anaesthesia was provided to the subjects' fingertips. In both conditions vision of the hand was prevented during movement. Anaesthesia affected mainly the kinematics of the first phase of grasping, that is, the finger-opening phase. This phase was lengthened and maximal finger aperture increased. In contrast, the duration of the successive phase (finger-closure) was poorly modified. The reaching component was also impaired by anaesthesia. Although the total extent of hand path and the spatial relations between the finger aperture and closure phases did not change between the two conditions, hand path variability increased. This occurred during transport deceleration phase and after the increase in variability of finger path. In addition, the whole movement was slowed down. The results of the present experiment suggest that tactile signals at the beginning and at the end of movement can be used to compute grasp time and to optimise grasp temporal parameters. Alternatively, signals from tactile receptors can be involved in encoding the position sense of the fingers. When this input is lacking, the control of grasp and in particular that of finger-opening phase can be impaired. Finally, the effect of the grasp impairment on the reaching component supports the notion that the coordination between reaching and grasping involves the whole temporal course of the two components.

Moving one's finger to a visually specified position: target orientation influences the finger's path.

It has previously been shown that, when subjects are instructed to move their finger slowly from one point to another the finger follows a path that deviates systematically from a straight line connecting the two points. The deviation depends on the angle between this fictive line and a line connecting the subject's finger with his body. In the present study, we examined whether the deviation also depends on the target's orientation. In two experiments, subjects were instructed to move a finger slowly towards five targets. We recorded the finger's movements. In one experiment, the targets were aligned. In the other, they were oriented radially around the starting point. Otherwise, conditions were the same. The difference in target orientation influenced the finger's path. Most importantly, when the targets were oriented radially around the starting point, the finger's path was straight. We conclude that pointing is more than moving the finger to a specified position.

Coordination of three-joint digit movements for rapid finger-thumb grasp.

Human thumb and index finger kinematics were examined for multiple repetitions of a simple grasp task as a means to evaluate motor planning and execution of these important hand movements. Subjects generated a rapid (approximately 90-ms duration) pinch movement of the index finger and thumb from an open-hand position. Approximately 400 repetitions were obtained from four naive subjects. The two-dimensional trajectory of the fingertip and the angular positions of the metacarpophalangeal (MP) and proximal interphalangeal (PIP) joints of the index finger were recorded along with the angular position of the thumb interphalangeal joint (TH). Individual joint angular positions were transduced using planar electrogoniometers of an exoskeletal linkage design. Except for consistent single-peaked joint angle and digit trajectory velocity profiles, most kinematic features of the grasp varied considerably across trials, including fingertip spatial position at contact, specific finger paths, finger and thumb path distances, finger and thumb peak tangential velocities, and 5) individual joint rotation magnitudes and peak velocities. However, this kinematic variability was not random. Variable TH angular positioning was paralleled by complementary two-dimensional variations in the finger path. These fingertip adjustments were accomplished by actively controlled, reciprocal angular positioning of the MP and PIP joints. Specifically, with natural reductions in thumb flexion, MP flexion was greater while PIP flexion was reduced and vice versa. These adjustments acted to minimize variations in the point contact of the finger on the thumb and yielded a robust and seemingly natural preference for finger-thumb contact at the more distal surfaces of the digits. The kinematic variability was not due to the finger and thumb movements being controlled independently of digit contact. The variable appositional movements of the finger and thumb and the associated contact force were generated as a single action. This was indicated by an absence of kinematic or force adjustments after contact, smooth digit trajectories with a single peak in their tangential velocities, and finger-thumb contact that consistently occurred well after peak velocity. Likewise, because the variability in the kinematics of the grasp was systematic, it apparently was not due simply to sloppiness or noise in motor execution.(ABSTRACT TRUNCATED AT 400 WORDS)