Development and Application of a Portable System to Reliably Measure Grip Forces Using Thin-Film Force Sensors

Accurate tracking of hand grip force is an important consideration needed for a robust understanding in the study of human biomechanics. One aspect where it proves useful is in hand-arm vibration, such as from gripping a power tool. Depending on how firmly the user is gripping the tool, they may change their exposure levels to the tool vibration, which can lead to potential disorders such as Hand-Arm Vibration Syndrome (HAVS). A small, battery powered portable force unit has been developed to supply power to, and condition, the signals from eight thin-film force sensors. This gives a better understanding of the grip force used on many different tool applications that were previously immeasurable. Using this information, knowledge can be gained in determining how much of a role grip force plays in the onset of the aforementioned disease. Using the portable force unit, two different applications are explored. The first uses an instrumented handle in conjunction with thin-film sensors to ascertain how well the thin-film sensors model the overall grip strength recorded by the handle. Using varying numbers of sensors to map the hand, a conversion factor was determined to calculate the actual grip force represented by the waveforms of the thin-film sensors. The observed results of this experiment indicated that the use of eight to four thin-film force sensors yield conversion factors that are similar, therefore using four sensors gives a similar estimated force response, while minimizing sensor bulk. The second application is in field work. Several grip force measurements were made in the field while subjects were using pneumatic power tools. A subject calibration of the thin-film sensors was performed using the same instrumented handle mentioned previously and the unit allowed for the thin-film sensors to be used in the actual tool use measurement. Using the conversion factors from the laboratory on the data collected in the field, a better understanding of grip force was obtained. This understanding is from a real work environment rather than a laboratory tool simulation conducted by lab personnel unfamiliar with the tool, which could bias the results. Applying this method of tracking grip force is expected to provide a better understanding of how grip force plays a role in HAVS and how tool handle designs can be improved

Med Eng Phys

Inverse dynamics models used to investigate musculoskeletal disorders associated with handle gripping require accurate phalangeal kinetics. Cylindrical handles wrapped with pressure film grids have been used in studies of gripping kinetics. We present a method fusing six degree-of-freedom hand kinematics and a kinematic calibration of a cylinder-wrapped pressure film. Phalanges are modeled as conic frusta and projected onto the pressure grid, automatically segmenting the pressure map into regions of interest (ROIs). To demonstrate the method, segmented pressure maps are presented from two subjects with substantially different hand length and body mass, gripping cylinders 50 and 70 mm in diameter. For each ROI, surface-normal force vectors were summed to create a reaction force vector and center of pressure location. Phalangeal force magnitudes for a data sample were similar to that reported in previous studies. To evaluate our method, a surrogate was designed for each handle such that when modeled as a phalanx it would generate a ROI around the cells under its supports; the classification F-score was above 0.95 for both handles. Both the human subject results and the surrogate evaluation suggest that the approach can be used to automatically segment the pressure map for quantifying phalangeal kinetics of the fingers during cylindrical gripping.CC999999/Intramural CDC HHS/United States2017-02-01T00:00:00Z26709291PMC483042

The Influence of Hand Tool Design on Hand Grip Strength: A Review

Hand is made up of bones, tendons, ligaments, nerves and blood vessels that can be easily debilitated and injured if the hand tool is not design ergonomically. Recently researchers have examined the effects of individual, environmental and occupational factors on hand grip strength. However, information on the influence of hand tool design on hand grip strength is still lacking. The aim of this paper is to provide a comprehensive review of factors influencing hand grip strength focusing more towards hand tool design factors. The authors searched the journal articles, book and guidelines from the online databases of Google Scholar, ScienceDirect and Pubmed. Fourteen factors of hand tools design were found to have significant effect on the hand grip strength.  The handle size shows the most significant factor for hand grip strength

Characteristic Of Elderly People Hand And Its Effect To Walking Stick Handle:A Case Study In Malacca

Hand is best known as an ultimate operative instrument, the hand helps in assisting human to grip,pinch,hold and others.According to the statistic in year 2015,the population of elderly people in Malaysia aged 60 years old and above was 2.8 million and by year 2035,the population projection of elderly people will up to 5.6 million.The projection figures give a preliminary picture on the demand for the usage of walking aids among elderly people.This study is to investigate the hand characteristics and biomechanics of elderly people and its effect to different design of handle of walking stick and propose handle of walking stick considering ergonomics aspects of elderly Malaysian.The sample of elderly people was taken from Rumah Seri Kenangan,Cheng, Malacca.They comprises of female and male of Malay, Chinese and Indian races,their age were sixty and above. Physical characteristics of hand such as:contact area, hand length,hand width,hand size,inside grip diameter and grip strength,grip force,was taken.Other than measuring physical dimension of hand,survey was also captures their opinion regarding the comfortability of using three types of handles walking stick design which were mostly used. Three types of walking stick handle were chosen based on market demand.There were positive correlations on hand length and hand size,hand size and inside grip diameter, hand size and grip strength.It has negative correlation for both genders for grip strength and age.Among the three handle of walking stick,the one that contribute to distributed force was handle Swan neck type followed by T-type handle and Crook type handle.On distribution of force among 5 location identified,the location on ulnar nerve area was the highest force.This was also confirmed by results of questionnaires and interview.For recommendation,the design of handle stick that give better comfort those that provide equally distributed force to hand.The size of handle should follow the hand size of elderly people.According to the result,the handle should have three different sizes.Padded handle stick would provide not only better grip but also comfort ability

Human engineering design criteria handbook for lunar scientific equipment

Human engineering design criteria handbook for lunar scientific equipmen

Review and Evaluation of Hand–Arm Coordinate Systems for Measuring Vibration Exposure, Biodynamic Responses, and Hand Forces

AbstractThe hand coordinate systems for measuring vibration exposures and biodynamic responses have been standardized, but they are not actually used in many studies. This contradicts the purpose of the standardization. The objectives of this study were to identify the major sources of this problem, and to help define or identify better coordinate systems for the standardization. This study systematically reviewed the principles and definition methods, and evaluated typical hand coordinate systems. This study confirms that, as accelerometers remain the major technology for vibration measurement, it is reasonable to standardize two types of coordinate systems: a tool-based basicentric (BC) system and an anatomically based biodynamic (BD) system. However, these coordinate systems are not well defined in the current standard. Definition of the standard BC system is confusing, and it can be interpreted differently; as a result, it has been inconsistently applied in various standards and studies. The standard hand BD system is defined using the orientation of the third metacarpal bone. It is neither convenient nor defined based on important biological or biodynamic features. This explains why it is rarely used in practice. To resolve these inconsistencies and deficiencies, we proposed a revised method for defining the realistic handle BC system and an alternative method for defining the hand BD system. A fingertip-based BD system for measuring the principal grip force is also proposed based on an important feature of the grip force confirmed in this study

Grip force and force sharing in two different manipulation tasks with bottles

Grip force and force sharing during two activities of daily living were analysed experimentally in 10 right-handed subjects. Four different bottles, filled to two different levels, were manipulated for two tasks: transporting and pouring. Each test subject’s hand was instrumented with eight thin wearable force sensors. The grip force and force sharing were significantly different for each bottle model. Increasing the filling level resulted in an increase in grip force, but the ratio of grip force to load force was higher for lighter loads. The task influenced the force sharing but not the mean grip force. The contributions of the thumb and ring finger were higher in the pouring task, whereas the contributions of the palm and the index finger were higher in the transport task. Mean force sharing among fingers was 30% for index, 29% for middle, 22% for ring and 19% for little finger. Practitioner Summary: We analysed grip force and force sharing in two manipulation tasks with bottles: transporting and pouring. The objective was to understand the effects of the bottle features, filling level and task on the contribution of different areas of the hand to the grip force. Force sharing was different for each task and the bottles features affected to both grip force and force sharing.We wish to thank the Fundació Caixa-Castelló and the Universi- tat Jaume I for financial support through project P1-1B2009-40 and the Spanish Ministry of Economy and Competitiveness and FEDER through project DPI2014-60635-R. With the financial support of the Department of Mechanical Engineering and Con- struction at the Universitat Jaume I, Mark Andrews helped the authors with the English language edition of the manuscript

Measurement ( Mahwah N J)

The use of a handheld adapter equipped with a tri-axial accelerometer is the most convenient and efficient approach for measuring vibration exposure at the hand-tool interface, especially when the adapter is incorporated into a miniature handheld or wrist-strapped dosimeter. To help optimize the adapter approach, the specific aims of this study are to identify and understand the major sources and mechanisms of measurement errors and uncertainties associated with using these adapters, and to explore their improvements. Five representative adapter models were selected and used in the experiment. Five human subjects served as operators in the experiment on a hand-arm vibration test system. The results of this study confirm that many of the handheld adapters can produce substantial overestimations of vibration exposure, and measurement errors can significantly vary with tool, adapter model, mounting position, mounting orientation, and subject. Major problems with this approach include unavoidable influence of the hand dynamic motion on the adapter, unstable attachment, insufficient attachment contact force, and inappropriate adapter structure. However, the results of this study also suggest that measurement errors can be substantially reduced if the design and use of an adapter can be systematically optimized toward minimizing the combined effects of the identified factors. Some potential methods for improving the design and use of the adapters are also proposed and discussed.CC999999/Intramural CDC HHS/United States2016-01-05T00:00:00Z26744580PMC470105

Estimating hand-grip forces causing Cumulative Trauma Disorder

Wearable sensors have garnered considerable interest because of their potential for various applications. However, much less has been studied about the Stretchsense pressure sensor characteristics and its workability for industrial application to prevent potential risk situations such as accidents and injuries. The proposed study helps investigate Stretchsense pressure sensors\u27 applicability for measuring hand-handle interface forces under static and dynamic conditions. The BendLabs sensors - a multi-axis, soft, flexible sensing system was attached to the wrist to evaluate the wrist angle deviations. In addition, the StretchSense stretch sensors were attached to the elbow joint to help estimate the elbow flexion/extension. The research tests and evaluates the real-time pressure distribution across the hand while performing given tasks and investigates the relationship between the wrist and elbow position and grip strength. The research provides objective means to assess the magnitudes of high pressures that may cause pressure-induced discomfort and pain, thereby increasing the hand\u27s stress. The experiment\u27s most significant benefit lies in its applicability to the actual tool handles outside the laboratory settings