Human Hand-arm System Research Articles

Modeling and control of dynamical biomechanical arm systems with elastic joints sensitive to the effect of an external load

In this study, a biomechanical model mimicking the human hand-arm system under heavy disk excitation is developed to define the stability threshold between the preload vibration and the stress of the human hand-arm system. The fully electromechanical system, consisting of a DC motor, a transmission system, and three discrete masses representing the upper arm, forearm, and hand lifting a heavy disk, is connected by shock absorbers and various springs. The challenge of mimicking the angular activity of the elbow joint in torsion and flexion was also included to assess its contribution to system stability and to study the absorption of mechanical energy in the human hand-arm system. Finally, the movements of the model were described by a differential matrix equation, and its analysis facilitates the understanding of the threshold of the chaotic behaviors observed in an oscillating arms system. Specifically, it explores how the motion of a DC motor can be regulated using a single controller parameter within the context of a multi-degree-of-freedom human hand-arm system. The study uses numerical integrations to analyze system behaviors, with an emphasis on the use of frequency spectra, Poincaré maps, and bifurcation diagrams for visualization and interpretation. The results indicate that the system exhibits chaotic behavior when subjected to certain conditions, particularly when the mass load exceeds 35 kg. Imposing motion on the mass block further intensifies the chaos, leading to manifestations such as strong oscillations and frequency-synchronization effects. These characteristics, exhibited by the idealized model, which imitates the human body through a mechanical model and computation of the motions of the body, play a vital role in various fields of ergonomics and sports biomechanics. Understanding the dynamic behaviors of such systems, especially in response to varying conditions, has significant implications for engineering applications.

Vibration transmissibility at male and female wrists of the human hand–arm system and modeling

The determination of standard values of vibration transmissibility at the wrist of the human body is very important to understanding vibration exposure and developing a valid model. In this work, the effects of human weight, gender, and other factors on the transmissibility of hand–arm vibration and vibration transmissibility in the [Formula: see text]-axis direction at the wrist site were randomly collected from 200 subjects (154 males and 46 females) as per the requirement of the standard ISO 10819. Moreover, the envelopes of the maximum and minimum values, as well as the mean and standard deviation of the vibration transmissibility at the wrist site, were obtained for both genders. Second, the effect of gender differences on the mean value of vibration transmissibility was analyzed. Finally, two three-degree-of-freedom (3-DOF) models of the hand–arm system were developed based on the average values of vibration transmissibility at the wrists of male and female subjects, respectively. The study revealed that the mean value of vibration transmissibility was greater in males than in females in the frequency range of 14–39 Hz. For the rest of the frequency ranges of females, their mean vibration transmissibility is greater than that of males, especially in the range 17–30 Hz. It was also observed that the vibration transmissibility of females is 10–18.5% smaller than that of males. The vibration transmissibility of females is greater than that of males by 40–83% when the frequencies are between 150 Hz and 250 Hz. The novelty of this proposed model is the prediction of model differences between males and females compared to other models that do so without considering gender differences. It is validated that the proposed modified model can be used to predict the vibration transmissibility of the wrist.

Influence of Coupling Forces and Body Posture on the Rotational Hand–Arm Impedance in yh Direction

This manuscript investigates the rotational mechanical impedance of the human hand–arm system with respect to vibration excitation around the gripping axis of the hand under the influence of body posture, gripping force, and push force. Knowledge of rotational mechanical impedance is required for deriving models of hand–arm biodynamics. These models are used in the validation of power tools to predict further vibrational human–machine interactions. In the current state of research, such models exist for translational but not rotational vibration excitation. Consequently, this study investigates the properties of a hand–arm system with respect to rotational vibration excitation. In the study, the rotational impedance of the hand–arm systems of 13 adults was measured at various gripping and push forces applied in different body postures. The setup of the test used in this study consisted of a shaker that applied rotational vibrations at certain frequencies to the subjects’ hand–arm systems via a cylindrical handle. The results of the study indicate a spring–damper dynamic of the hand–arm system. The gripping force strongly influences the magnitude of rotational impedance across the frequency spectrum. Regarding push force and posture, no corresponding influence could be determined. The results suggest that the frictional contact between the hand and handle might confer a damping effect.

Influence of coupling forces on the mechanical impedance of the hand-arm system during rotational vibration excitation around the xh-axis

The research presented in this paper focuses on the determination of the rotational mechanical impedance of the human hand-arm system under rotational vibration excitation, applied via the knob-shaped handle. During the development of power tools, the interaction between the power tool and the hand-arm system must be simulated. This requires accurate models of the hand-arm system's biodynamics. The current state of research provides such models for translational vibrations, but are limited when also considering rotational vibrations. To enable the development of such models, the study investigates the biodynamics of the hand-arm system for rotational vibration excitation. Therefore, the rotational impedance of 21 subjects was measured in a study. In the study, a knob-shaped measuring handle, whereby the subjects applied different combinations of gripping and push forces to the handle, vibrated the hand-arm system of the subjects rotationally. The results show that a higher gripping force results in a higher magnitude of rotational mechanical impedance, while the push force does not seem to influence the rotational impedance. The missing influence of the push force on the rotational impedance may be caused by the alignment between hand position, force direction, and excitation axis. The findings of this study extend the overall knowledge of rotational mechanical impedance for simulating the hand-arm system in power tool development. In regards to the rotational vibration exposure when performing sanding tasks, the results suggest that a frictional connection between the hand and the power tool handle reduces the vibration exposure of the hand-arm system.

A statistical model to predict the occurrence of blunt impact injuries on the human hand-arm system

Biomechanical limits based on pain thresholds ensure safety in workplaces where humans and cobots (collaborative robots) work together. Standardization bodies’ decision to rely on pain thresholds stems from the assumption that such limits inherently protect humans from injury. This assumption has never been verified, though. This article reports on a study with 22 human subjects in which we studied injury onset in four locations of the hand-arm system using an impact pendulum. During the tests, the impact intensity was slowly increased over several weeks until a blunt injury, i.e., bruising or swelling, appeared in the body locations under load. A statistical model, which calculates injury limits for a given percentile, was developed based on the data. A comparison of our injury limits for the 25th percentile with existing pain limits confirms that pain limits provide suitable protection against impact injuries, albeit not for all body locations.

Effect of high level grip-and push force and elevated arm posture on the zh-axis hand-arm impedance

In this study, we investigated the effect of grip forces, push forces and two arm postures on the biodynamic response of the human hand-arm system for vibration excitation along the forearm axis. Knowledge about the biodynamic response, in this case the mechanical impedance, is important for understanding the dynamic human-machine interaction and developing human models. The current state of research lacks information about the effect of high grip forces, push forces, and an overhead hand-arm posture on the mechanical impedance. In this study, we measured the mechanical impedance of 30 subjects with an electromechanical shaker in translational direction along the forearm axis. We investigated the influence of grip-forces (30 & 135 N), push-forces (50 & 110 N), arm postures (shoulder flexion 0° & 90°) as well as the respective effect sizes in the range of 10–500 Hz. The investigated factors have a significant influence (p < .01) depending on the vibration frequency. The arm posture had a significant influence in the low frequency range with a weak effect size, while push forces affected the MI in a medium frequency range with a medium to strong effect size. Grip forces had a strong effect at low and high frequencies. The findings from this study contribute to the general understanding of hand-arm dynamics but also serve as an input for the development of mechanical and simulation models of the human hand-arm system which can be used to assess vibrations during development of hand held machinery.

An Investigation of the Effect of Hand-Arm Posture and Grip Force on Vibration Transmission Rate of Human Hand-Arm System

An Investigation of the Effect of Hand-Arm Posture and Grip Force on Vibration Transmission Rate of Human Hand-Arm System

A biomechanical model to predict hand-arm vibration when using different vibration damping gloves

Occupational exposure to the hand-transmitted vibration causes health problems and difficulties in the operators of hand-held power tools. This results in the reduction of manpower and increased costs in terms of compensations remunerated to the affected workers. A principal means to control hand-arm vibration is the use of vibration damping gloves. The primary focus of the current study is to develop biomechanical model of the human bent hand-arm system to predict vibration transmissibility when using different vibration damping gloves. The transmissibility plot was obtained by solving the equations of motion of the biomechanical model considering mass, stiffness and damping coefficient of the gloves. The transmissibility plot obtained from the model indicated that there was no significant reduction in finger vibrations at excitation frequencies less than 100 Hz, even if anti-vibration gloves are used. However, the gloves could appreciably reduce finger vibrations at higher frequencies. The observed response from the model was in agreement with the experimental studies reported in the prior literature suggesting the acceptability of the model for analysing vibration transmissibility characteristics of the human hand-arm system. The model can thus be used to evaluate engineering methods for vibration exposure control during operation of hand-held vibrating tools.

Incidence of Predisposing Factors on the Human Hand-arm Response with Flexed and Extended Elbow Positions of Workers Subject to Different Sources of Vibrations

Purpose This paper analyses the predisposing factors that affect the time response of the hand–arm system. Predisposing factors are the method of tool use, tool type, source of power, the mass of tool, workpiece held in hand, dimensions of the handle, grip force and push force, and dynamic and thermal properties of handgrips. Methods This research considers the variability of the time response of the hand–arm system with respect to predisposing factors evaluated in 5 working conditions. The mathematical model consists of a distributed parameter representation in the form of a beam characterized by a continuous distribution of the mass, damping, and elasticity of the physical properties of the human and–arm system. The mathematical model considers the action of the extensor muscles of the elbow. The experimental investigations evaluate the forced vibrations of the human hand–arm system in work conditions. Novelty in research The analysis of predisposing factors on the human hand–arm response with flexed and extended elbow positions of workers subject to different sources of vibrations represents the novelty in this research. Operators assume different human hand–arm postures when using manual power tools. The human hand–arm with flexed and extended elbow positions are the postures of workers evaluated in this research. The research on postures of workers aims to provide an evidence base for prevention. Another important objective is to provide a better overview of the extent of the occupational burden of workers. Work-related diseases include musculoskeletal disorders. Results Posture factors of the human hand–arm system and predisposing of occupational hand–transmitted vibration exposures are considered to estimate the response of human hand–arm positions in the time domain. Conclusions Mathematical model and experimental investigations provide a better evaluation of health risks and muscle actions associated with exposure to hand–transmitted vibration from power tools in work conditions.

Measurement of the Hand Transmitted Vibration of the Human Hand Arm System During Operation of a Hand Tractor.

Operators of hand tractors are exposed to high levels of hand transmitted vibration (HTV). This vibration, which can be both irksome and hazardous to human health, is imparted to the operator via his or her hands and arms. However, a standardized method for measuring HTV of hand tractors has yet to be defined. The aim of the study was to present an experimental method for the investigation of the biodynamic response and vibration transmissibility of the hand-arm system during the operation of a hand tractor in a stationary mode. Measurements were performed with ten subjects using three grip forces and three handle vibration levels to examine the influences of the hand pressure and frequency on hand transmitted vibration (HTV). The results indicate that the tightness of grip on the handle influences the vibration response of the hand-arm system, especially at frequencies between 20 and 100 Hz. The transmission of lower frequencies in the hand-arm system was relatively unattenuated. In comparison, attenuation was found to be quite marked for higher frequencies during the operation of the hand tractor. The vibration transmissibility to different parts of the hand-arm system decreased with the increase of the distance from the vibration source. The proposed methodology contributes to the collection of consistent data for the evaluation of operator vibration exposure and the ergonomics development of hand tractors.

Measurement of the Hand Transmitted Vibration of the Human Hand Arm System During Operation of a Hand Tractor

Measurement of the Hand Transmitted Vibration of the Human Hand Arm System During Operation of a Hand Tractor

An Experimental Study of the Influence of Hand-Arm Posture and Grip Force on the Mechanical Impedance of Hand-Arm System

In order to investigate the effects of hand-arm posture, grip force, push force, and vibration excitation intensity on the mechanical impedance of human hand-arm system, a test system with a self-developed vibration handle has been prepared. Based on the testing system, the mechanical impedance of the hand-arm system of seven Chinese adult males were tested and calculated under the random vibration excitation with the frequency of 10–1000 Hz. The results reveal that when the frequency is lower (&lt;40 Hz), the hand-arm system with an elbow angle of 180o produces a higher mechanical impedance; when the frequency ranges from 40 Hz to 100 Hz, the hand-arm system with an elbow angle of 90o generates a higher mechanical impedance; while when the frequency is higher (&gt;100 Hz), the hand-arm posture seems to have no obvious effect on the mechanical impedance. Higher grip or push force would increase the frequency corresponding to the peak value of the mechanical impedance and often correspond to a higher mechanical impedance in a specific frequency range (30–200 Hz). When the frequency is lower (&lt;140 Hz), vibration intensity has certain effects on the mechanical impedance of the hand-arm system. In conclusion, vibration intensity does not directly affect the mechanical impedance, but an increase in grip or push force often causes an increase in mechanical impedance and a higher frequency that corresponds to the peak of mechanical impedance.

The influence of human interaction on the vibration of hand-held human-machine systems – The effect of body posture, feed force, and gripping forces on the vibration of hammer drills

In hand-held human machine systems the biodynamic response of the human hand arm system influences the overall dynamic behavior. The biodynamic response of the hand arm system is affected by several influencing factors. These influencing factors include the feed force, body posture, gripping force, and anthropometric properties. In present studies the importance of the gripping force on the biodynamic response is highlighted. In the state of the art; however, the magnitude of gripping forces as well as the influence of the human factors body posture and feed force on hammer drills for a larger group of professional users is unclear. To analyze the influence that these human factors have on hammer drill vibrations, a study with 15 professional power tool test personnel has been conducted. Characteristic gripping force values have been measured (Median: 84 N–156 N at the main handle, 10 N–30 N on the auxiliary handle) for different feed forces (100 N, 150 N, 200 N) and body postures. Then the influence of body posture, feed force, and gripping force on the hammer drill vibration is determined. A significant influence of the body posture (ANOVA: p = .003, r = .367) on the RMS acceleration of the main handle was observed. Furthermore, the feed force has a significant influence on the vibration of the hammer-drill for some groups. The data also demonstrates that for increasing gripping forces, the RMS of the acceleration and frequency weighted acceleration ahv on the main and auxiliary handle decrease. The findings of this study represent a starting point for the development of adjustable hand-arm models for the reproducible vibration assessment of power tools.

Nonlinear Biodynamic Models of the Hand-arm System and Parameters Identification using the Vibration Transmissibility or the Driving-point Mechanical Impedance

This study aims at deriving nonlinear expressions of the transmissibility and the driving-point mechanical impedance (DPMI) of two nonlinear biodynamic hand-arm models having active restoring and dissipative parameters. It aims also in computing explicitly the non-directly measurable stiffness and damping coefficients of the human hand-arm system (HAS). Multivariate Pade approximants are used to express the dependence of the HAS mechanical properties on various influencing factors. The harmonic balance method is used to derive analytical expressions of the transmissibility and the DPMI. Then, the models parameters are identified by minimizing constrained error functions between the theoretical DPMI or transmissibility and the measured data. The developed workflow is applied to three experimental data sets of Z-direction vibrations where the excitation frequency and/or the grip force are varied. Using the ISO-10068 (2012) limit DPMI values versus the excitation frequency, we derived upper and lower limits of the overall stiffness coefficient and damping ratio for the human HAS. Furthermore, the model reproduces with high accuracy experimental measurements of the transmissibility, the DPMI and the vibration power absorption.

Development and Analysis of Human Hand-Arm System Model for Anti-Vibration Isolators

The potential health injuries associated with human hand-transmitted mechanical vibration which caused during driving vehicles, and operating on hand-held power tools. In this study five Degree-of-Freedom (DOF) human hand-arm system model is developed to analyze HAS model in terms of acceleration responses. The study analysed one of the possible protective way to reduce hand-transmitted vibration by using the anti-vibration isolators to machine handle. This study presents biomechanical models consisting deflection patterns due to masses at the finger, palm-wrist and upper-arm, corresponding to different modes of vibration, subject to z-axis vibration. A MATLAB-SIMULINK based model is also developed to determine the effect of vibration transmission from machine tool handle. The anti-vibration isolators have been introduced as a gripper of machine tool handle and simulation results shows significantly better damping characteristics and reduction of the vibration transmission effect to HAS.

Stress and strain distributions in the human hand-arm system using finite element analysis

This study presents stress and strain distributions in the human hand-arm system exposed to vibrations using finite element (FE) models. Frequency weightings at shoulder, elbow, wrist and palm based on stress and strain distributions were proposed. The stress/strain-based frequency weightings around the shoulder and elbow are comparable with that reported in the International Organization for Standardization ISO 5349-1, Mechanical vibration and shock– Measurement and evaluation of human exposure to mechanical vibration – part 1: General requirements, 2001. However, stress/strain-based frequency weightings around the palm and wrist are different above 20 Hz from the weighting reported by the International Standard Organization. This study suggests the need for different frequency weightings for the assessment of the potential injury of different components of the hand-arm vibration syndrome.

Assessing the influence of hand-arm posture on mechanical responses of the human hand during drilling operation

Drilling is one of the important metal cutting processes in the industrial sectors. Though there are several research studies exclusively pertaining to drilling mechanism and the implications on materials, there are research voids that pertain to the driller’s hand-arm posture and the corresponding mechanical responses during the process. Considering the vitality of the ergonomics involved, the objective is framed to estimate the stresses acting on the hand while operating handheld drilling machine by different subjects and investigate the effects of various hand-arm postures on the stresses transmitted to the hands. Finger TPS—wireless tactile force sensor device—is employed for measuring the force exerted at the fingers while operating handheld cordless drilling machine. The nature of vibration transmitted to the human hand-arm system is affected by the contact force variation between a vibrating tool handle and the hand. The transmitted vibration will impose the stresses on the anatomical structure of the hand-arm system. In the present study, the dynamic response of a human hand to exert force during drilling task is analysed by three-dimensional finite element (FE) model of the human hand of a normal male. The model is developed from 3D reconstruction of CT scan images using the segmentation software, Mimics. The FE model contains the essential anatomical structures of a human hand. It includes both linear and nonlinear elements to represent rigid and elastic parts of the hand like the bones, tissues etc. Refined FE model is properly meshed, and analysis is carried out using finite element code ABAQUS. Preliminary results of the numerical analysis utilizing the developed model and qualitative evaluation are presented. Stress values are the highest while drilling in the extended forearm with the elbow at an angle of 180° and are followed by drilling objects located at a height above shoulder level.

The influence of a human hand-arm system on the vibrational dynamic behaviour of a compliant mechanical structure

The aim of this study is to provide an approach to predicting human influence on a compliant mechanical structure using a substructuring technique. Substructuring techniques allow us to obtain detailed information on the vibrational behaviour of an assembly of structures by characterization of each structure separately. In this manuscript, a hand-arm system is coupled with a vibrating structure using a substructuring technique. A lightweight and compliant vibrating beam is used to demonstrate the concept. To demonstrate the feasibility of accurately predicting the hand-arm systems’ influence on the beam, we selected one position and tested it using four push forces. The characteristics of the hand-arm system for each configuration were coupled with the dynamic characteristics of the beam only over a frequency range of [5; 300] Hz. For each of the four configurations, the coupling predicts the influence of the hand on the vibrational behaviour of the beam. Reliable predictions were obtained for the vibrational behaviour of the assembly. The results indicate that the substructuring approach predicted the vibrational behaviour of the hand-arm-beam assembly with less than 3% error.

Modal parameters of the human hand-arm using finite element and operational modal analysis

This study presents a finite element (FE) model of the human hand-arm system to derive natural frequencies and mode shapes. The FE model is calibrated by considering modal parameters obtained from experimental vibration analyzed by using operational modal analysis (OMA) and transmissibility. Modal and harmonic analyses of the FE model are performed for two boundary conditions. The first one considers fixed shoulder condition while the second one introduces the trunk in order to permit motion of the shoulder. The results show that the natural frequencies of the second model that permits shoulder motion are comparable with those determined from measurements. Especially, the natural frequency about 12 Hz, which is corresponding to the frequency of maximum weight in ISO-5349-1 (2001), is not present in the model with fixed shoulder condition, while it appears in the second model. The results of the present study suggest that improved finite element models of the human hand-arm system may reveal hand-arm injury mechanism, the understanding of which may assist in deriving appropriate frequency weightings for the assessment of different components of the hand-arm vibration syndrome.

Distributed vibration power absorption of the human hand-arm system in different postures coupled with vibrating handle and power tools

This study presents vibration power absorption (VPA) of different hand-arm substructures in the bent-arm and extended arm postures excited by broadband random and power tool vibrations. VPAs are estimated using biomechanical models of the hand-arm system derived from both the driving-point mechanical impedance and distributed vibration transmissibility. VPAs due to the vibrations of selected hand-held power tools are also estimated. The results show that distributed VPAs of the arms are greater below 25 Hz than those of the hand (fingers and palm) for both postures, while the hand VPAs are greater above 100 Hz, although the values are smaller than those below 25 Hz. The power absorbed during the extended arm posture is about 2.5 times greater than the power absorbed with the bent-arm posture for similar hand forces and vibration magnitude. Similar trends are observed in distributed VPAs due to broadband random as well as typical tool excitations, while the VPA due to tool vibration revealed peaks near the operating frequencies of the power tools and their harmonics. Furthermore, the percentage of power absorbed in different hand-arm substructures was dependent on the operating speed of the power tools, the higher the operating speed the higher the power absorbed in the hand and vice versa. The results showed relatively lower VPA values in the fingers and palm in the 60–160 Hz range than those obtained for the arms in the 5–16 Hz range. The study revealed the need for different frequency weightings for assessment of potential injury risk of different hand-arm substructures. Relevance to industryOperators of hand-held power tools are exposed to hand-transmitted vibration and the associated potential injuries. This study showed that the extended arm posture should be avoided when operating hand-held power tools because large vibration power is absorbed in the human hand-arm system, which may cause hand-arm injury.