Finger Contact Research Articles

Grasp Input Optimization Taking Contact Position and Object Information Uncertainties into Consideration

This paper presents a novel approach for grasp optimization considering contact position and object information uncertainties. In practice, it is hard to grasp an object at the designated or planned contact positions, as errors in measurement, estimation, and control usually exist. Therefore, we first formulate the influences of contact uncertainties on joint torques, contact wrenches, and frictional condition. We then include external wrench uncertainties in the required external wrenches set. Based on this formulation, we define the linear grasp optimization problem for two kinds of frictional contact models-frictional point contact and soft finger contact-so that we can successfully grasp an object even if deviations in contact point, object weight, and center of mass occur. The validity of our approach is shown by means of numerical examples and the result of experiments.

Simulation Tool for Equivalent Circuit Modeling of Photovoltaic Devices

We describe an open-source simulation tool for the modeling of photovoltaic devices with equivalent circuit networks. Our SpiceGUI interconnects devices with known current voltage characteristics and calculates the current density–voltage curve of the combined device. The SpiceGUI is written as hybrid Octave/MATLAB code and has a flexible graphical user interface. It supports batch simulations with the SPICE tools LTspice, NGspice, and SMARTspice. The available postprocessing functions include convenient batch parameter plots and power loss analysis diagrams. We present two simulation examples. The first example simulates a solar cell with front contact fingers. It assists the reader in understanding the SpiceGUI unit tree and serves as starting point for the development of custom models. This first example also shows that the SpiceGUI yields reliable results, even for very demanding models that exceed 4 GB working memory. The second example models back-contacted thin-film silicon solar cells. We use measured <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J _{\rm sc}\hbox{--}V _{\rm oc}$</tex></formula> curves as input data for the current sources of the network. Additional resistive elements complete the network. The simulated JV curves of the combined device agree well with the measured JV curves. The distributed nature of the resistances is essential to describing the shape of the measured JV curves.

Two‐Finger Gestures for 6DOF Manipulation of 3D Objects

AbstractMultitouch input devices afford effective solutions for 6DOF (six Degrees of Freedom) manipulation of 3D objects. Mainly focusing on large‐size multitouch screens, existing solutions typically require at least three fingers and bimanual interaction for full 6DOF manipulation. However, single‐hand, two‐finger operations are preferred especially for portable multitouch devices (e.g., popular smartphones) to cause less hand occlusion and relieve the other hand for necessary tasks like holding the devices. Our key idea for full 6DOF control using only two contact fingers is to introduce two manipulation modes and two corresponding gestures by examining the moving characteristics of the two fingers, instead of the number of fingers or the directness of individual fingers as done in previous works. We solve the resulting binary classification problem using a learning‐based approach. Our pilot experiment shows that with only two contact fingers and typically unimanual interaction, our technique is comparable to or even better than the state‐of‐the‐art techniques.

Optimization Investigation on Contact Finger Seal Performances Based on a Fuzzy Game Approach

Optimization Investigation on Contact Finger Seal Performances Based on a Fuzzy Game Approach

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.

Impact of screen printing silver paste components on the space charge region recombination losses of industrial silicon solar cells

An approved measurement method for evaluating space charge region recombination (SCR-recombination) induced by the screen printed front side metallization is applied for industrial solar cells with aluminum back surface field (Al-BSF) on monocrystalline Czochralski silicon (Cz-Si). The H-patterned base grid of all processed solar cells is screen printed with a commercially available front side silver paste, ensuring sufficiently good contacting and therefore good electrical performance of the solar cells. Additionally, irregular contact fingers are realized between the regular contact fingers of the base grid by applying different screen printing layouts with commercially available front side pastes to increase the front side metallization fraction linearly as well as by applying various test pastes for the layout with the highest metallization fraction. Well-known components of glass frits as lead oxide, zinc oxide, bismuth oxide and boron oxide can affect SCR-recombination. Therefore we fabricated test pastes with these specific paste/glass frit components. By applying this test structure, a comparable qualitative evaluation of SCR-recombination with respect to the specific paste component is demonstrated. Quantitative evaluations regarding the electrical performance of the solar cells as well as related microstructural investigations are presented.

Transparent and flexible force sensor array based on optical waveguide

This paper suggests a force sensor array measuring contact force based on intensity change of light transmitted throughout optical waveguide. For transparency and flexibility of the sensor, two soft prepolymers with different refractive index have been developed. The optical waveguide consists of two cladding layers and a core layer. The top cladding layer is designed to allow light scattering at the specific area in response to finger contact. The force sensor shows a distinct tendency that output intensity decreases with input force and measurement range is from 0 to -13.2 dB.

Detection of nitro-organic and peroxide explosives in latent fingermarks by DART- and SALDI-TOF-mass spectrometry

The ability of two mass spectrometric methods, surface-assisted laser desorption/ionization-time of flight-mass spectrometry (SALDI-TOF-MS) and direct analysis in real time (DART-MS), to detect the presence of seven common explosives (six nitro-organic- and one peroxide-type) in spiked latent fingermarks has been examined. It was found that each explosive could be detected with nanogram sensitivity for marks resulting from direct finger contact with a glass probe by DART-MS or onto stainless steel target plates using SALDI-TOF-MS for marks pre-dusted with one type of commercial black magnetic powder. These explosives also could be detected in latent marks lifted from six common surfaces (paper, plastic bag, metal drinks can, wood laminate, adhesive tape and white ceramic tile) whereas no explosive could be detected in equivalent pre-dusted marks on the surface of a commercial lifting tape by the DART-MS method due to high background interference from the tape material. The presence of TNT and Tetryl could be detected in pre-dusted latent fingermarks on a commercial lifting tape for up to 29 days sealed and stored under ambient conditions.

MONTE CARLO ASSESSMENT OF THE FINGER SHALLOW DOSE FROM DIRECT CONTACT WITH A MICROCENTRIFUGE TUBE CONTAINING COMMON BIOTECHNOLOGY ISOTOPES IN SOLUTION

Eppendorf tubes often are used in biomedical research labs and contain radioactive tracers. Although the associated direct contact finger doses are typically small, it is suggested (and in line with the principle of ALARA) to handle these tubes from the cap of the tube. When containing radioactive material, handling a tube near the bottom conical section would unnecessarily increase the skin dose to the fingers. This investigation modeled a 2.0-mL Eppendorf tube containing various individual beta emitting isotopes commonly used in a biomedical research environment (i.e., (14)C, (3)H, (131)I, (32)P, and (35)S) to determine the skin dose when directly handling the tube at the cap end and when handling it at the bottom conical section. The primary goal of this paper is to assess how significantly this dose is altered by handling geometry. The skin dose to a single finger was calculated with Monte Carlo simulations using MCNP5 and determined at a depth of 0.007 cm(2) in water averaged over 10 cm as described in 10CFR20. Results show that the dose rate may vary by as much as a factor of 700 depending on handling geometry.

Handling objects in old age: forces and moments acting on the object

We measured the external moments and digit-tip force directions acting on a freely moveable object while it was grasped and manipulated by old (OA) and young (YA) adults. Participants performed a grasp and lift task and a precision orientation (key-slot) task with a precision (thumb-finger) grip. During the grasp-lift task the OA group misaligned their thumb and finger contacts and produced greater grip force, greater external moments on the object around its roll axis, and oriented force vectors differently compared with the YA group. During the key-slot task, the OA group was more variable in digit-tip force directions and performed the key-slot task more slowly. With practice the OA group aligned their digits, reduced their grip force, and minimized external moments on the object, clearly demonstrating that the nervous system monitored and actively manipulated one or more variables related to object tilt. This was true even for the grip-lift task, a task for which no instructions regarding object orientation were given and which could tolerate modest amounts of object tilt without interfering with task goals. Although the OA group performed the key-slot task faster with experience, they remained slower than the YA group. We conclude that with old age comes a reduced ability to control the forces and moments applied to objects during precision grasp and manipulation. This may contribute to the ubiquitous slowing and deteriorating manual dexterity in healthy aging.

Immersed finger-type indium tin oxide ohmic contacts on p-GaN photoelectrodes for photoelectrochemical hydrogen generation

In this study, we demonstrated photoelectrochemical (PEC) hydrogen generation using p-GaN photoelectrodes associated with immersed finger-type indium tin oxide (IF-ITO) ohmic contacts. The IF-ITO/p-GaN photoelectrode scheme exhibits higher photocurrent and gas generation rate compared with p-GaN photoelectrodes without IF-ITO ohmic contacts. In addition, the critical external bias for detectable hydrogen generation can be effectively reduced by the use of IF-ITO ohmic contacts. This finding can be attributed to the greatly uniform distribution of the IF-ITO/p-GaN photoelectrode applied fields over the whole working area. As a result, the collection efficiency of photo-generated holes by electrode contacts is higher than that of p-GaN photoelectrodes without IF-ITO contacts. Microscopy revealed a tiny change on the p-GaN surfaces before and after hydrogen generation. In contrast, photoelectrodes composed of n-GaN have a short lifetime due to n-GaN corrosion during hydrogen generation. Findings of this study indicate that the ITO finger contacts on p-GaN layer is a potential candidate as photoelectrodes for PEC hydrogen generation.

Determining Force-Closure Grasps Reachable by a Given Hand

The paper presents an approach to find contact points on an object surface that are reachable by a given hand and such that the resulting grasp satisfies the force-closure condition. This is a very common problem that still requires a practical solution. The proposed method is based on the computation of a set of independent contact regions on the object boundary such that a finger contact on each region produces a force-closure grasp, and then this set of regions is iteratively recomputed while looking for a set of contact points that are reachable by a given hand. The search is done guided by a cost function that indicates the proximity of the hand fingertips to a candidate set of grasping contact points. The approach has been implemented for the Schunk Anthropomorphic Hand and planar objects, and application examples are included to illustrate its performance.

Hydrogen gas generation using n-GaN photoelectrodes with immersed Indium Tin Oxide ohmic contacts

An n-GaN photoelectrochemical (PEC) cell with immersed finger-type indium tin oxide (ITO) ohmic contacts was demonstrated in the present study to enhance the hydrogen generation rate. The finger-type ITO ohmic contacts were covered with SiO₂ layers to prevent the PEC cell from generating leakage current. Using a 1M NaCl electrolyte and external biases, the typical photocurrent density and gas generation rate of the n-GaN working electrodes with ITO finger contacts were found to be higher than those with Cr/Au finger contacts. The enhancement in photocurrent density or gas generation rate can be attributed to the transparent ITO contacts which allowed the introduction of relatively more photons into the GaN layer. No significant corrosion was observed in the ITO layer after the PEC process compared with the Cr/Au finger contacts which were significantly peeled from the GaN layer. These results indicate that the use of n-GaN working electrodes with finger-type ITO ohmic contacts is a promising approach for PEC cells.

Parameters Optimization for the Triplet High Voltage Disconnect Self-Elastic Contact Fingers Based on the New Cu-Cr Alloy Strip

Based on the performance of new Cu-Cr alloy strip, triplet self-elastic contact fingers by traditional copper material were analyzed. Through the finite element numerical simulation and DOE sensitivity analysis, it is determined that thickness was the key parameter which impacts the contact fingers structure. Then the structure parameters were optimized. The results show that after optimization, thickness of contact fingers by traditional copper material decrease to 3.43 mm from 5 mm, the maximum equivalent stress is 315.37 MPa, the maximum shear stress is 181.24 MPa, the maximum deformation is 2.55mm, and the mass is reduced about 30%.

Improved Tactile Shear Feedback: Tactor Design and an Aperture-Based Restraint.

Tactile feedback could replace or augment visual and auditory communication in a range of important applications. This paper advances the field of tactile communication by presenting performance data on a variety of tactors and a finger restraint that is suitable for use in portable devices. Tactors, the contact elements between the device and the skin, and finger restraints were evaluated using a tangential skin displacement direction identification task. We tested tactors of three sizes and two different textures. Rough textured tactors improved communication accuracy compared to smooth tactors, but tactor size did not have a statistically significant effect. Aperture-based restraints of three sizes were evaluated on both the index finger and the thumb. The aperture-based restraint was effective when used on both the index finger and the thumb, with performances on par with our previously tested thimble-based restraint. Participants performed better with larger apertures than with smaller apertures, but there was no interaction between aperture size and finger size, meaning that the same aperture could be used with a range of finger sizes. Subjects' perceptual acuity varied with stimulus direction. We discuss the effects of contact force, finger size, and differences in perceptual acuity between the index finger and thumb.

Contrasting effects of finger and shoulder interpersonal light touch on standing balance

Sway is reduced by light nonsupporting touch between parts of the body and a fixed surface. This effect is assumed to reflect augmentation of sensory cues for sway by point-of-contact reaction forces. It has been shown that movement of the contact surface can increase sway relative to an earth-fixed contact. Light touch contact with another person, for example, holding hands, affords a moving contact due to partner sway. We asked whether interpersonal light touch (IPLT) would increase sway relative to standing alone. We expected effects on sway to vary as a function of the site of contact and the postural stability of each partner. Eight pairs of participants, standing in either normal bipedal or tandem Romberg stance with eyes closed and using IPLT (finger to finger or shoulder to shoulder) or no contact, provided 4 trials of 30-s duration in each of 12 posture-touch combinations. Sway (SD of the rate of change of upper trunk position at C7) was reliably less with IPLT compared with no contact, with two exceptions: in normal stance, shoulder contact with a partner in tandem stance, and in tandem Romberg stance, finger contact with a partner in the same stance, increased sway. Otherwise, the reduction in sway was greater with shoulder than with finger contact. Measures of interpersonal synchronization based on cross-correlations and coherence analysis between the partners' C7 movements suggest different control factors operate to reduce sway in IPLT with the hand or shoulder contact.

Assessment on assorted hyper-elastic material models applied for large deformation soft finger contact problems

Modeling of soft finger contact mechanics is a prerequisite for gripper design. Realism of soft finger deformations depends extremely on the selection of appropriate hyper-elastic material model for soft materials. The essential criterion for a good mathematical model for hyper elasticity is its ability to match the measured strain energy curves under different deformations over a large range. Selecting an appropriate material law for a given material combination is one of the most difficult tasks in soft finger contact modeling. The present study is devoted for comparing seven popular hyper-elastic non-linear material models (Mooney–Rivlin, Ogden, Yeoh, Neo-Hookean, Gent, Polynomial and Aruda–Boyce model) and selection of the most appropriate model based on experimental data for modeling of soft contact problems. Present results clearly reveal that Ogden and Neo-Hookean model are more suitable for these problems and in line with the experimental results. Finite element technique is employed for critical comparison of various hyper-elastic material models.

Human finger contact with small, triangular ridged surfaces

Ridges are often added to surfaces to improve grip of objects such as sports equipment, kitchen utensils, assistive technology, etc. Although considerable work has been carried out to study finger friction generally, not much attention has been paid to understanding and modelling the effects of surface texture. Previous studies indicate that at low roughness values friction decreases as roughness increases, but then a sharp increase is seen after a threshold level of roughness is reached. This is thought to be due to interlocking. In this study an analytical model was developed to analyse the different mechanisms of friction of a fingerpad sliding against triangular-ridged surfaces that incorporated adhesion, interlocking and hysteresis. Modelling was compared with experimental results from tests on five different triangular-ridged surfaces, manufactured from aluminium, brass and steel. Model and experiment compared well. The study showed that at low ridge height and width the friction was dominated by adhesion. However, above a ridge height of 42.5 μm, interlocking friction starts to contribute greatly to the overall friction. Then at a height of 250 μm, a noticeable contribution from hysteresis, of up to 20% of the total friction, is observed.

Coordination of Contact Forces During Multifinger Static Prehension

This study investigated the effects of modifying contact finger forces in one direction-normal or tangential-on the entire set of the contact forces, while statically holding an object. Subjects grasped a handle instrumented with finger force-moment sensors, maintained it at rest in the air, and then slowly: (1) increased the grasping force, (2) tried to spread fingers apart, and (3) tried to squeeze fingers together. Analysis was mostly performed at the virtual finger (VF) level (the VF is an imaginable finger that generates the same force and moment as the four fingers combined). For all three tasks there were statistically significant changes in the VF normal and tangential forces. For finger spreading/squeezing the tangential force neutral point was located between the index and middle fingers. We conclude that the internal forces are regulated as a whole, including adjustments in both normal and tangential force, instead of only a subset of forces (normal or tangential). The effects of such factors as EFFORT and TORQUE were additive; their interaction was not statistically significant, thus supporting the principle of superposition in human prehension.

Discovering affordances that determine the spatial structure of reach-to-grasp movements

Extensive research has identified the affordances used to guide actions, as originally conceived by Gibson (Perceiving, acting, and knowing: towards an ecological psychology. Erlbaum, Hillsdale, 1977; The ecological approach to visual perception. Erlbaum, Hillsdale, 1979/1986). We sought to discover the object affordance properties that determine the spatial structure of reach-to-grasp movements--movements that entail both collision avoidance and targeting. First, we constructed objects that presented a significant collision hazard and varied properties relevant to targeting, namely, object width and size of contact surface. Participants reached-to-grasp objects at three speeds (slow, normal, and fast). In Experiment 1, we explored a "stop" task where participants grasped the objects without moving them. In Experiment 2, we studied "fly-through" movements where the objects were lifted. We discovered the object affordance properties that produced covariance in the spatial structure of reaches-to-grasp. Maximum grasp aperture (MGA) reflected affordances determined by collision avoidance. Terminal grasp aperture (TGA)--when the hand stops moving but prior to finger contact--reflected affordances relevant to targeting accuracy. A model with a single free parameter predicted the prehensile spatial structure and provided a functional affordance-based account of that structure. In Experiment 3, we investigated a "slam" task where participants reached-to-grasp flat rectangular objects on a tabletop. The affordance structure of this task was found to eliminate the collision risk and thus reduced safety margins in MGA and TGA to zero for larger objects. The results emphasize the role of affordances in determining the structure and scaling of reach-to-grasp actions. Finally, we report evidence supporting the opposition vector as an appropriate unit of analysis in the study of grasping and a unit of action that maps directly to affordance properties.