Pin Stiffness Research Articles

EMG feedback improves grasping of compliant objects using a myoelectric prosthesis

BackgroundClosing the control loop in myoelectric prostheses by providing artificial somatosensory feedback is recognized as an important goal. However, designing a feedback interface that is effective in realistic conditions is still a challenge. Namely, in some situations, feedback can be redundant, as the information it provides can be readily obtained through hearing or vision (e.g., grasping force estimated from the deformation of a compliant object). EMG feedback is a non-invasive method wherein the tactile stimulation conveys to the user the level of their own myoelectric signal, hence a measurement intrinsic to the interface, which cannot be accessed incidentally.MethodsThe present study investigated the efficacy of EMG feedback in prosthesis force control when 10 able-bodied participants and a person with transradial amputation used a myoelectric prosthesis to grasp compliant objects of different stiffness values. The performance with feedback was compared to that achieved when the participants relied solely on incidental cues.ResultsThe main outcome measures were the task success rate and completion time. EMG feedback resulted in significantly higher success rates regardless of pin stiffness, indicating that the feedback enhanced the accuracy of force application despite the abundance of incidental cues. Contrary to expectations, there was no difference in the completion time between the two feedback conditions. Additionally, the data revealed that the participants could produce smoother control signals when they received EMG feedback as well as more consistent commands across trials, signifying better control of the system by the participants.ConclusionsThe results presented in this study further support the efficacy of EMG feedback when closing the prosthesis control loop by demonstrating its benefits in particularly challenging conditions which maximized the utility of intrinsic feedback sources.

Seismic Performance Assessment of a Pin-bearing Restraint System for Curved Bridge

The traditional restraint systems limit the deformation of curved bridge under temperature load, which results in radial and tangential secondary internal forces in the bridge. This paper proposes a pin-bearing restraint system (PBRS) for curved bridge, which can relax the rotational deformation of curved bridge under temperature load. Its configuration and working mechanism are illustrated. The finite element model of a curved bridge with PBRS is established using ANSYS software, and nonlinear time history analysis is conducted. The pounding force and pounding number between pin and slot under ground motion are analyzed. The pin stiffness, the gap and the ratio of upper structure mass to lower structure mass are selected for parametric study. The results show that the pounding force and pounding number present dramatic changes with pin stiffness. As the pin stiffness increases, the pounding force presents a logarithmic linear tendency, and the pounding number shows a reduce tendency. Gap has little influence on pounding force and pounding number. The radial pounding force and pounding number increase with the increase of mass ratio.

Dynamical load sharing behaviors of heavy load planetary gear system with multi-floating components

To investigate the dynamical load sharing behaviors of multi-floating components in the heavy load planetary gear system, a multi-floating planetary gear system that includes a floating central component and a quasi-floating planet flexible supporting pin is employed. Then a 21 degree of freedom lumped parameters dynamical model of this system is presented to study the dynamical load sharing behaviors. Some influencing factors, such as supporting stiffness, positions error of sun or carrier, and external input load are analyzed on the dynamical load sharing of the planetary gear system with multi-floating components. The results demonstrate that the load sharing condition of the system is best when both the sun gear and planet gears are multi-floating at the same time. When the planet gear position errors remain constant, reducing the flexible pin stiffness of planet gear or increasing external input load can effectively improve the load sharing. These conclusions are verified by the relevant experiments.

The nonlinear effects of flexible pins on wind turbine gearboxes

The structure of flexible pin-type planetary gear systems used in wind turbine gearboxes can improve the load sharing ability of planets while saving space unlike straddle-type carriers. However, the nonlinear dynamic characteristic of this type of system is not fully developed. This work presents a coupled lumped-parameter dynamic model to demonstrate nonlinear effects. Gear contact loss nonlinearity and bearing clearance nonlinearity are integrated into this dynamical model, and the effects of flexible pins on the nonlinear dynamic responses are discussed. The conclusions made are as follows: lower flexible pin stiffness can significantly reduce nonlinear effects; when pin stiffness is increased, contact loss still occurs in positions of strong vibration even if the planet gear bearings have higher orders of magnitude of tangential load in the wind turbine gearbox; dynamic response peaks are asymmetric with a frequency sweep; only left oblique "Soft" jumps occur, and the right oblique “Hard” jump phenomena rarely occur; planet gear supporting the bearing clearance exists; and vibration chaos occurs in positions of strong vibration.

A New Methodology for Scaling the Mechanics of Pin-reinforcement in Composite Sandwich Structures under Compression using Digital Image Correlation

There is a great deal of interest in understanding the mechanics in pin-reinforced composite sandwich structures. In particular, characterizing the relationship of the mechanics in smaller to larger specimens due to changes in the pin response can expedite the development of more advanced models, as well as the assessment of new materials and processing conditions. In this investigation, specimens with a conventional symmetric pin configuration anchoring into each facesheet have been experimentally characterized under compressive loading. The effect of specimen size on the compressive response has been investigated through the number of active pins under loading. The stress–strain response of these structures exhibit initially high compressive stiffness followed by a significant load shedding and flow stress. The transition in the mechanical behavior is attributed to the failure of reinforced pins under a combination of axial compression and transverse bending due to their orientation relative to the facesheets. As the size of a specimen is decreased, the effective stiffness and strength decrease due to a decrease in effective pin stiffness. It was found that these effects on the compressive stress can be scaled through a stress scaling factor derived from the change in the structure of the specimen due to the number of active versus inactive pins per unit of area, which is scaled by the pin density related to the pin basis and spacing for the corresponding pin configuration. Using Digital Image Correlation (DIC), it was then possible to account for these size effects on compressive strain directly through the pin deformations. A stiffness scaling factor could then be determined from a model of a beam in bending under axial and transverse loading that was correlated to the DIC displacements to determine the effective pin stiffness and corresponding stiffness scaling factor for strains. A stretched exponential relationship was also found to describe the scaling of the effective pin stiffness with the number of active pins. The compressive stress–strain response was then corrected to show that similar scaled properties could be obtained for the compressive modulus. The Poisson’s ratio was also obtained from the DIC strains averaged over the full specimen, and a scaling relation similar to that for the effective pin stiffness was developed.

Handling sticky Resin by Stingless Bees: Adhesive Properties of Surface Structures

Many Stingless Bees (Hymenoptera: Meliponini) like Tetragonisca angustula collect resin to defend their nests against intruders like ants or Robber Bees. Small portions of resin are attached to intruders bodies and extremities causing their immobilization. It has been observed that resin is removed easily from the bee's mandible but adheres strongly to the intruder's cuticle. We tested the hypothesis that resin sticks lesser to the mandibles of Stingless Bees than to the surface of intruders due to special surface structures or adhesive properties of these structures. The surface structures of the mandible of T. angustula and the trochanter of Camponotus sericeiventris were studied by scanning electron microscopy. To measure adhesion properties, selected surfaces were fixed on a fine glass pin and withdrawn from a glass tip covered with resin. The deformation of the glass pin indicates adhesion forces operating between the resin and the selective surface. The absolute value of the forces is computed from the glass pin's stiffness. It has been shown that resin sticks more to the smooth mandible of the bee than to the structured trochanter of the ant. A new hypothesis to be tested says that the bees might lubricate their mandibles with nectar or honey to reduce the resin's adhesion temporarily.

Effect of flexible pin on the dynamic behaviors of wind turbine planetary gear drives

Flexible pins eliminate the need for straddle mounting, and therefore enable the maximum possible number of planets to be used for any particular epicyclic ratio of power transmission systems. Having more planet gears will significantly increase the input torque density. In this type of design, the pin stiffness and position tolerances are important parameters as they affect the dynamic performances significantly. The present study addresses this issue by modeling, the design of double cantilevered flexible pin, and analyzing the contributions of pin stiffness and misalignment applying the lumped parameter approach. The proposed model formulates the coupled lateral-torsional dynamic response of a planetary spur gear, including the effects of mesh stiffness and phasing as a function of pin error. The resultant equations of motion are applied to examine the effects of pin stiffness and position errors on the natural modes and structural dynamic response. The effects of pin stiffness on deviation of the tooth contact forces of the sun-planet and ring-planet gear pairs are analyzed to understand the relationship between mesh characteristic and input speed variations. The calculated supporting forces of the planet gear are examined to understand the load sharing characteristic due to pin errors, pin stiffness and input load of the power transmission system.

Mechanical evaluation of a tapered thread-run-out half-pin designed for external skeletal fixation in small animals

An in vitro mechanical study was performed to compare the stiffness, maximum load, and cyclic load-to-failure of a new external fixation half-pin design utilizing a tapered thread-run-out (TRO) feature with currently available positive profile thread (PP) half-pins. Five different sizes of each of the two pin types were evaluated. Under static loading, TRO pins were significantly stiffer and had a higher maximum load compared to the similar sized PP pins (p <0.0001 for all comparisons). In cyclic fatigue testing, TRO pins lasted 2.3- to 4.9-fold more cycles than PP pins of similar size (p <0.0001 for all comparisons). The increased pin stiffness and improved cyclic lifespan provided by TRO pins may be especially valuable in the stabilization of biologically and mechanically challenging fracture cases where healing is prolonged.

Influence of Planet Pin Stiffness on Load Sharing in Planetary Gear Drives

Others have done significant work on the subject of load sharing among the planets of planetary gear drives; a brief review of that work is presented. Little work has been done, however, to evaluate the utility of the Hicks type flexible planet pins in improvement of load sharing in a planetary gear stage. This work shows the potential value of the three variations of the Hicks type flexible planet pin used on cantilever carriers, and a new design of a low spring constant planet pin that can be used on straddle type carriers. This is done by the calculation of the spring constants of gear meshes, bearings, and various designs of planet pins using the finite element method for a specific design of a planetary gear stage with spur gears and eight planets. The result showed significant differences. Low spring constant flexible pins are shown to have significantly superior load sharing characteristics.

Friction-induced oscillations of a slider: Parametric study of some system parameters

A typical frictionally excited pin on disk system is modeled as a basis for vibration control. The model is based on chosen experimental setup parameters. The analysis incorporates normal, tangential and torsional degrees of freedom. The effect of varying both the normal force and the pin stiffness on the response of the pin subsystem in all directions is investigated numerically. A detailed parametric study shows that the operating condition namely the normal force and the rotational speed have a remarkable influence on the response. A correlation between measured and calculated system response is presented, that supports the validity of the presented model. The dynamic characteristics of the system, namely stiffness of the pin in both normal and torsional direction, have no significant effect on its response, while its tangential stiffness has a minor effect.

DBEM and FEM analysis on non-linear multiple crack propagation in an aeronautic doubler-skin assembly

The performance of a riveted patch repair, applied on a cracked panel, is simulated by using both a commercially available boundary element code (BEASY) and a finite element code (ANSYS). A two-dimensional stress analysis on a single-sided repaired configuration is performed by both methodologies; consequently, the occurrence of out-of-plane bending and its effect on the through-thickness stress intensity factor (SIF) variation is neglected. The connection between the two layers (patch and panel) is realised by 32 rivets, with through-cracks initiated on the most loaded holes. Special elements are used to model the crack: discontinuous elements in the dual boundary element method (DBEM) approach or quarter point elements in the finite element method (FEM) approach. Different loading configurations are considered depending on the presence of a biaxial or uniaxial remote load and the non-linear hole/rivet contact is simulated by gap elements. The most stressed skin holes are highlighted, and the effect of a through crack from such holes is analysed in terms of SIFs and stress redistribution. The accuracy in SIFs assessment by DBEM and FEM and the respective computational and pre-processing efforts are determined. Such a two-dimensional analysis allows us a straightforward pre-processing phase, and very short run times are needed. A peculiar arrangement of the pin configuration in the DBEM analysis allows us to take into account the real in-plane plate stiffness and the transversal pin stiffness, even in a 2D analysis (this is straightforward by using FEM).

Deformations and stresses in pin-loaded tubes under axial tension

The results of an experimental study of the deformations and stresses developed in a series of pin-loaded cylindrical tubes subjected to an axial tensile load are presented and discussed. The effects of variations in the pin/tube diameter ratio and the position of the pin axis relative to the tube end are established for a particular tube thickness/diameter ratio (0.08), and the effects of variations in this ratio are described for two particular pin-tube configurations. The work also includes an assessment of the effects of lubrication at the pin-tube interfaces, pin clearance in the pin-holes, pin stiffness and restraint of radial deformations in the tube.

Analysis of an Interference-Fit Pin Connection

Under a simplifying but reasonably justified assumption of noninterference from the adjoining pins, a mathematical analysis of an interference-fit pin connection in a backplane for the initial contact force is presented. Effects of pin shape, stiffness, interference fit, hole shape, and plate material are included in the study. A closed form solution is obtained for estimating the initial contact force in the joint, thus eliminating the need for complicated numerical techniques generally used for such complex problems. Numerical results of initial radial forces for different pin and plate parameters are presented. An example of a lanced compliant pin is discussed.

Epicyclic Gear Vibrations

The natural frequenices of in-plane vibration of a single planetary gear stage are analyzed. The gear tooth stiffnesses are approximated as linear springs. The effect of planet pin stiffness on the natural frequencies is evaluated. Rotation of the carrier gives rise to a system with periodic coefficients which is solved by means of Floquet’s theory. The rotation of the carrier appears to suppress the nonaxisymmetric modes which are present in the system with nonrotating carrier.