1,361 research outputs found
Generating Secure and Gentle Grip on Soft Substrates
No full textGeneration of grip on soft tissue in the surgical field is most commonly done with forceps that generate friction grip, that is, the translation of normal (pinch) forces into shear forces. Errors made with these surgical grippers are often force-related: applying too low pinch forces results in slipping of the tissue out of the gripper, and too high pinch forces may lead to tissue damage. One possible solution for generating tissue grip that is secure yet gentle is the adhesive grip. In this case, contact between tissue and gripper is maintained by attracting gripper-tissue interactions, and gripping strength does not depend on the applied pinch forces. Inspiration for the design of such a gripper can be derived from the tree frog, an animal that uses adhesive grip to grip on a range of substrates in its habitat. The main aim of this thesis is to translate grip-generating principles used by tree frogs into designs of artificial adhesives that can generate firm yet gentle grip on soft substrates. The designs of the artificial adhesives in this thesis are inspired by two important characteristics of the tree frog’s attachment apparatus: the hierarchical surface pattern on the tree-frog toe-pad and reinforcing fibrillar structures located inside the pad. Specifically, the aim of this thesis is to mimic function rather than form, and focuses on mechanisms underlying the tree-frog attachment apparatus to satisfy two main requirements for strong grip: (1) contact formation and (2) preservation of the formed contact.Medical Instruments & Bio-Inspired Technolog
Improving the Meta-Grip: Redesigning for unsupervised use
No full textThe Meta-Grip is a tool for climbers to measure hand and finger strength. A climber uses the Meta-Grip by hanging on either a sloper or crimp. The Meta-Grip measures the force through a load cell and transfers the data to a computer where the data can be viewed and analyzed. The current Meta-Grip is built for research. Because of this, the current Meta-Grip cannot be used unsupervised, the embodiment needs improvements and the price of 2520 euros for the costs is too high for the intended market. The current Meta- Grip can only do measurements, an addition to its functionalities would be the ability to also train on the Meta-Grip. This let to the following goal for redesigning the Meta-Grip: “Redesign the Meta-Grip in such a way that it becomes an affordable and recognizable tool that measures finger and hand strength and provides immediate and understandable feedback to the climber, that can be used unsupervised by climbers and is an addition to the currently available training tools.“. To redesign the Meta-Grip, the design process is structured in four phases: analysis, ideation, concept design and final validation. The following methods were used: literature research, online market research, online surveys, sketching, prototyping, user testing, hosting creative sessions and expert interviews. The redesigned Meta-Grip is a product-service system. The Meta-Grip, made for fanatic climbers, has a range in holds that differ in type and difficulty. Holds are available in alder wood for skin friendliness or polyurethane coated with quartz sand for high friction, to the user’s discretion. With two load cells and a Bluetooth module , a connection can be established to the mobile phone application of the Meta-Grip. This application, the service, is used to execute measurements, follow exercises and training plans and determine climbing goals. A button on the Meta-Grip allows users to turn the Meta-Grip on and connect the Meta-Grip via Bluetooth to the application on their phone. To instruct the user on how to use the Meta-Grip before the Bluetooth connection is available, instructions are placed on the left side of the Meta-Grip. The system is powered by a 9V battery. The installation of the Meta-Grip is made such that it will fit any normal climbing gym with two M10 bolts. This research has shown the potential of a redesigned Meta-Grip. Through the application, the Meta-Grip can be used unsupervised and changing the design has made the Meta-Grip more versatile and recognizable for climbers. The cost price is estimate at 120 euros, making it a large price reduction. The next step is to further elaborate the concept and all parts of the product-service system to make it ready for launching the Meta-Grip to the market. <br/
Gelders Rivierdijkenplan: Hoofdlijnennotitie
No full textIn januari 1993 besloten Gedeputeerde Staten dat er een beleidsplan voor de rivierdijken moest komen: het Gelders Rivierdijkenplan (GRIP). Het voorliggende document, de hoofdlijnennotitie GRIP, is een eerste stap op weg naar dat plan. Zij is bedoeld om in een vroeg stadium de hoofdpunten van het toekomstig beleid te bespreken met betrokkenen en belanghebbenden. Het resultaat van die discussie, de vastgestelde hoofdlijnennotitie, dient vervolgens als vertrekpunt voor de opstelling van het rivierdijkenplan. De hoofdlijnennotitie bevat vijf hoofdstukken. Het eerste hoofdstuk omschrijft doel en opzet van de notitie en de procedure die moet leiden tot het Gelders Rivierdijkenplan. Het tweede hoofdstuk schetst achtergronden en (voor)geschiedenis van de dijkverbetering. Het derde hoofdstuk bevat een probleemanalyse met daarin opmerkingen over de verschillende dijkfuncties en -waarden, de afstemming van dijkverbeteringsplannen op andere plannen, de besluitvormingsprocedure bij dijkverbetering, en het dijkbeheer en - onderhoud. Hoofdstuk vier behandelt status en doelstellingen van het plan. De hoofdlijnen van het toekomstig waterkeringsbeleid worden uiteengezet in hoofdstuk vijf. Ten slotte zijn vijf bijlagen en een overzichtskaart van de stand van de rivierdijkverbeteringswerken toegevoegd. In de notitie zijn de dijken langs de randmeren buiten beschouwing gelaten omdat deze buiten het rivierengebied vallen
Childhood socioeconomic position and objectively measured physical capability levels in adulthood: a systematic review and meta-analysis
No full text<p><b>Background:</b> Grip strength, walking speed, chair rising and standing balance time are objective measures of physical capability that characterise current health and predict survival in older populations. Socioeconomic position (SEP) in childhood may influence the peak level of physical capability achieved in early adulthood, thereby affecting levels in later adulthood. We have undertaken a systematic review with meta-analyses to test the hypothesis that adverse childhood SEP is associated with lower levels of objectively measured physical capability in adulthood.</p>
<p><b>Methods and Findings:</b> Relevant studies published by May 2010 were identified through literature searches using EMBASE and MEDLINE. Unpublished results were obtained from study investigators. Results were provided by all study investigators in a standard format and pooled using random-effects meta-analyses. 19 studies were included in the review. Total sample sizes in meta-analyses ranged from N = 17,215 for chair rise time to N = 1,061,855 for grip strength. Although heterogeneity was detected, there was consistent evidence in age adjusted models that lower childhood SEP was associated with modest reductions in physical capability levels in adulthood: comparing the lowest with the highest childhood SEP there was a reduction in grip strength of 0.13 standard deviations (95% CI: 0.06, 0.21), a reduction in mean walking speed of 0.07 m/s (0.05, 0.10), an increase in mean chair rise time of 6% (4%, 8%) and an odds ratio of an inability to balance for 5s of 1.26 (1.02, 1.55). Adjustment for the potential mediating factors, adult SEP and body size attenuated associations greatly. However, despite this attenuation, for walking speed and chair rise time, there was still evidence of moderate associations.</p>
<p><b>Conclusions:</b> Policies targeting socioeconomic inequalities in childhood may have additional benefits in promoting the maintenance of independence in later life.</p>
The impact of grip strength recovery on grip force accuracy in chronic stroke
No full text2020 Summer.Includes bibliographical references.Decreased grip force accuracy and grip strength are two well-documented grip impairments that impede upper extremity function after stroke. Grip force accuracy is essential to perform precise motor actions in everyday life. Further, grip strength represents the ability to produce maximal grip force in a short duration of time and constitutes as a hallmark of upper extremity recovery in chronic stroke. Adequate grip strength and grip force accuracy are both important for regaining motor function after stroke. Despite this, no study has investigated whether the recovery of grip strength influences improvements in force accuracy. Purpose: Therefore, the purpose of the study was to investigate the impact of grip strength recovery on grip force accuracy in chronic stroke patients. Methods: We recruited two distinct stroke groups with low (less than 60%) and high (60% or more) grip strength recovery. The grip strength recovery was computed as the percent of paretic grip strength relative to nonparetic grip. A total of thirty-three participants, eleven in low strength recovery group (age 64 ±14.8 years; 6 females and 5 males), eleven in high strength recovery group (age 65.9 ± 9.9 years, 7 females and 4 males) and eleven age matched controls (age 69.6 ± 9.8 years, 4 females and 7 males) participated in the study. To examine the impact of grip strength recovery on grip force accuracy, all participants performed two tasks; 1) maximum voluntary contraction (MVC) and 2) dynamic force tracking task, using each hand. We quantified grip strength as the maximum force produced in the MVC task. Further, we assessed force accuracy by measuring root mean square error relative to the absolute target force. Result: The grip strength recovery in low strength recovery stroke group (27.1 ± 17.7)% was lower compared to the high strength recovery group (92.4 ± 24.9)% and controls (94.9 ±18.9)%. A significant main effect of Group [F (2, 30) = 34.53, p 0.05). A significant interaction between Group×Hand, [F (2, 30) = 7.21, p < 0.05, partial ղ2 = 0.33] demonstrated that the relative RMSE of paretic hand was significantly increased in low strength recovery stroke group compared to the high strength recovery (p < 0.05). Importantly, the relative RMSE of paretic hand in high strength recovery group was significantly greater than the control group's non-dominant hand (p < 0.05). Overall, a significant negative relationship between grip strength recovery and paretic relative RMSE (r = -0.598, p = 0.003) was found when investigating correlations in both groups together. In low strength recovery group, we found a negative association between the grip strength recovery and paretic relative RMSE, (r = -0.552, p = 0.078). However, in high strength recovery group, we found no association between the grip strength recovery (r = 0.308, p = 0.357). Conclusion: Grip strength recovery and force accuracy follow differential patterns of improvement for low and high strength recovery stroke groups. In chronic stroke survivors with strength recovery less than 60%, grip strength recovery is associated with grip force accuracy. However, in chronic stroke survivors with strength recovery more than 60%, the grip force accuracy may still be impaired despite near-normal grip strength recovery. After substantial gain in grip strength recovery, interventions that enhance grip force accuracy may be needed to improve the upper-extremity function. Our study results suggest, after improvement in strength, patients need additional interventions such as exergaming that will train force accuracy, to help them use this regained strength more meaningfully
The SF-36: a simple, effective measure of mobility disability for epidemiological studies
No full textBackgroundMobility disability is a major problem in older people. Numerous scales exist for the measurement of disability but often these do not permit comparisons between study groups. The physical functioning (PF) domain of the established and widely used Short Form-36 (SF-36) questionnaire asks about limitations on ten mobility activities.ObjectivesTo describe prevalence of mobility disability in an elderly population, investigate the validity of the SF-36 PF score as a measure of mobility disability, and to establish age and sex specific norms for the PF score.MethodsWe explored relationships between the SF-36 PF score and objectively measured physical performance variables among 349 men and 280 women, 59-72 years of age, who participated in the Hertfordshire Cohort Study (HCS). Normative data were derived from the Health Survey for England (HSE) 1996.Results32% of men and 46% of women had at least some limitation in PF scale items. Poor SF-36 PF scores (lowest fifth of the gender-specific distribution) were related to: lower grip strength; longer timed-up-and-go, 3m walk, and chair rises test times in men and women; and lower quadriceps peak torque in women but not men. HSE normative data showed that median PF scores declined with increasing age in men and women.ConclusionOur results are consistent with the SF-36 PF score being a valid measure of mobility disability in epidemiological studies. This approach might be a first step towards enabling simple comparisons of prevalence of mobility disability between different studies of older people. The SF-36 PF score could usefully complement existing detailed schemes for classification of disability and it now requires validation against them
Estimating driver time-varying neuromuscular admittance through LPV model and grip force
No full textHumans can rapidly change their low-frequency arm dynamics (i.e., stiffness) to resist forces or give way to them. Quantifying driver’s time-varying arm dynamics is important for the development of steer-by-wire systems and haptic driver support systems. Conventional LTI identification, and even time-varying techniques such as wavelets, fail to capture rapidly-varying low-frequency dynamics. In this study, we propose to estimate driver admittance in real-time, using grip force measurement of the hands on the steering wheel and linear parameter-varying (LPV) modeling techniques. We hypothesized that grip force is strongly correlated to neuromuscular admittance, and can serve as an appropriate scheduling variable for an LPV model. We performed an experiment in which 18 subjects performed a boundary tracking task, and applied torque perturbations to the steering wheel to perform a baseline LTI identification. Six different boundary widths were used to evoke changes in admittance, while their grip force was measured with pressure gloves. A global LPV model is identified by linear interpolation between the local LTI models identified for each boundary width. The estimated stiffness and damping parameters varied proportionally with the grip force. Although small between-subject variations in grip force levels are found, we conclude that grip force can indeed serve as an appropriate scheduling variable for a global LPV model, which is capable of tracking fast-changing admittance changes. Future work focuses on using the LPV model in realistic driving tasks, permitting admittance estimates to be obtained without the need to apply external disturbance torques on the steering wheel.Human-Robot InteractionControl & SimulationControl & Operation
Effects of Carpal Tunnel Syndrome on Dexterous Manipulation Are Grip Type-Dependent
No full textabstract: Carpal tunnel syndrome (CTS) impairs sensation of a subset of digits. Although the effects of CTS on manipulation performed with CTS-affected digits have been studied using precision grip tasks, the extent to which CTS affects multi-digit force coordination has only recently been studied. Whole-hand manipulation studies have shown that CTS patients retain the ability to modulate multi-digit forces to object mass, mass distribution, and texture. However, CTS results in sensorimotor deficits relative to healthy controls, including significantly larger grip force and lower ability to balance the torques generated by the digits. Here we investigated the effects of CTS on multi-digit force modulation to object weight when manipulating an object with a variable number of fingers. We hypothesized that CTS patients would be able to modulate digit forces to object weight. However, as different grip types involve the exclusive use of CTS-affected digits (‘uniform’ grips) or a combination of CTS-affected and non-affected digits (‘mixed’ grips), we addressed the question of whether ‘mixed’ grips would reduce or worsen CTS-induced force coordination deficits. The former scenario would be due to adding digits with intact tactile feedback, whereas the latter scenario might occur due to a potentially greater challenge for the central nervous system of integrating ‘noisy’ and intact tactile feedback. CTS patients learned multi-digit force modulation to object weight regardless of grip type. Although controls exerted the same total grip force across all grip types, patients exerted significantly larger grip force than controls but only for manipulations with four and five digits. Importantly, this effect was due to CTS patients’ inability to change the finger force distribution when adding the ring and little fingers. These findings suggest that CTS primarily challenges sensorimotor integration processes for dexterous manipulation underlying the coordination of CTS-affected and non-affected digits.The article is published at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.005375
Estimating an LPV model of neuromuscular admittance with grip force as scheduling parameter
No full textDevelopment of adaptive haptic shared control system requires understanding of the adaptive nature of the driver’s neuromuscular system. In this study, linear parameter varying modeling techniques are proposed to identify changes in the admittance of the driver’s arm. The admittance describes the relation between the torque applied to the steering wheel and steering wheel angle output. By conducting two experiments it is investigated whether grip force applied to the steering wheel serves as an appropriate scheduling variable for a LPV model. In our approach, first tracking tasks with torque perturba- tions applied to the steering wheel are performed with varying boundary widths to evoke changes in admittance. The relation between grip force and admittance is investigated by estimating neuromuscular stiffness and damping parameters and measuring the force applied to the steering wheel using pressure gloves. An LPV model is identified by linear interpolation between LTI models identified for each condition. Second, a driving task is performed in a fixed-base driving simulator to analyze the variance in grip force and changes in admittance between wide and narrow roads. The results of the driving task are used to assess the validity of the LPV model during driving tasks. It was found that the stiffness and damping parameters varied proportionally with the grip force. Although small variations in grip force levels are found between subjects, it is concluded that grip force is an appropriate scheduling variable for an LPV model. The relation between grip force and admittance was similar during driving tasks compared to the tracking tasks. The derived LPV model accurately describes the changes in the neuromuscular system over the range of grip force variations observed during the driving task. For further validation of the LPV model in the time-domain it is recommended to use time- varying boundary tasks.Aerospace EngineeringControl & Simulatio
Tangential Torque Effects on the Control of Grip Forces When Holding Objects With a Precision Grip
No full text Kinoshita, Hiroshi, Lars Bäckström, J. Randall Flanagan, and Roland S. Johansson. Tangential torque effects on the control of grip forces when holding objects with a precision grip. J. Neurophysiol. 78: 1619–1630, 1997. When we manipulate small objects, our fingertips are generally subjected to tangential torques about the axis normal to the grasp surface in addition to linear forces tangential to the grasp surface. Tangential torques can arise because the normal force is distributed across the contact area rather than focused at a point. We investigated the effects of tangential torques and tangential forces on the minimum normal forces required to prevent slips (slip force) and on the normal forces actually employed by subjects to hold an object in a stationary position with the use of the tips of the index finger and thumb. By changing the location of the object's center of gravity in relation to the grasp surface, various levels of tangential torque (0–50 N⋅mm) were created while the subject counteracted object rotation. Tangential force (0–3.4 N) was varied by changing the weight of the object. The flat grasp surfaces were covered with rayon, suede, or sandpaper, providing differences in friction in relation to the skin. Under zero tangential force, both the employed normal force and the slip force increased in proportion to tangential torque with a slope that reflected the current frictional condition. Likewise, with pure tangential force, these forces increased in proportion to tangential force. The effects of combined tangential torques and tangential forces on the slip force were primarily additive, but there was a significant interaction of these variables. Specifically, the increase in slip force for a given increment in torque decreases as a function of tangential force. A mathematical model was developed that successfully predicted slip force from tangential torque, tangential force, and an estimate of coefficient of static friction in the digit-surface interface. The effects of combined tangential torques and forces on the employed normal force showed the same pattern as the effects on the slip force. The safety margin against frictional slips, measured as the difference between the employed normal force and the slip force, was relatively small and constant across all tangential force and torque levels except at small torques (<10 N⋅mm). There was no difference in safety margin between the digits. In conclusion, tangential torque strongly influences the normal force required for grasp stability. When controlling normal force, people take into account, in a precise fashion, the slip force reflecting both tangential force and tangential torque and their interaction as well as the current frictional condition in the object-digit interface. </jats:p
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