Human Hand-arm System Research Articles

A COMPARISON OF BIODYNAMIC MODELS OF THE HUMAN HAND–ARM SYSTEM FOR APPLICATIONS TO HAND-HELD POWER TOOLS

The biodynamic response characteristics of various mechanical models of the human hand and arm system, reported in the literature, are evaluated in terms of their driving-point mechanical impedance modulus and phase responses. The suitability of the reported models for applications in realizing a mechanical simulator and assessment of vibration behavior of hand-held power tools is examined using three different criteria. These include the ability of the model to characterize the driving-point mechanical impedance of the human hand–arm system within the range of idealized values presented in ISO-10068 (1998); the magnitude of model deflection under a static feed force; and the vibration properties of the human hand and arm evaluated in terms of natural frequencies and damping ratios. From the relative evaluations of 12 different models, it is concluded that a vast majority of these models cannot be applied for the development of a mechanical hand–arm simulator or the assessment of dynamic behavior of the coupled hand–tool system. The higher order models, with three and four degrees of freedom, in general, yield impedance characteristics within the range of idealized values, but exhibit excessive static deflections. Moreover, these models involve very light masses (in the 1·2–4·8 g range), and exhibit either one or two vibration modes at frequencies below 10 Hz. The majority of the lower order models yield reasonable magnitudes of static deflections but relatively poor agreement with idealized values of driving-point mechanical impedance.

Hand-transmitted vibration and biodynamic response of the human hand-arm: a critical review.

Hand-arm vibration syndrome (HAVS) has been associated with prolonged exposure to vibration transmitted to the human hand-arm system from hand-held power tools, vibrating machines, or hand-held vibrating workpieces. The biodynamic response of the human hand and arm to hand transmitted vibration (HTV) forms an essential basis for effective evaluations of exposures, vibration-attenuation mechanisms, and potential injury mechanisms. The biodynamic response to HTV and its relationship to HAVS are critically reviewed and discussed to highlight the advances and the need for further research. In view of its strong dependence on the nature of HTV and the lack of general agreement on the characteristics of HTV, the reported studies are first reviewed to enhance an understanding of HTV and related issues. The characteristics of HTV and relevant unresolved issues are discussed on the basis of measured data, proposed standards, and measurement methods, while the need for further developments in measurement systems is emphasized. The studies on biodynamic response and their findings are grouped into four categories based on the methodology used and the objective. These include studies on (1) through-the-hand-arm response, expressed in terms of vibration transmissibility; (2) to-the-hand response, expressed in terms of the force-motion relationship of the hand-arm system; (3) to-the-hand biodynamic response function, expressed in terms of vibration energy absorption; and (4) computer modeling of the biodynamic response characteristics.

Transmission of vibration energy to different parts of the human hand-arm system.

The aim of this study was to investigate the transmission of vibration energy to three selected points along the hand and arm (knuckle, wrist and elbow) and to compare the energy transmission for two different kinds of vibration exposures, i.e. random and sinusoidal. The transmission of vibration energy was estimated for ten subjects during exposure to random (within the frequency range 20-5000 Hz) and sinusoidal vibration at eight different frequencies (20, 40, 80, 160, 320, 630, 1250 and 1600 Hz). The random and sinusoidal vibrations had a frequency-weighted acceleration level of 3 m/s2. The energy transmission was determined by simultaneous vibration measurements at the vibrating handle and in the hand-arm system. The measurements were made with a laser-velocity transducer and specially constructed equipment. The grip and feed forces were held constant at 40 N. The results show that the energy transmission decreases with the distance from the source. The results also show that the energy transmission is dependent on the frequency for the random vibration exposures. No clear frequency dependence of the energy transmission could be found for the sinusoidal vibrations. It may also be concluded that there are differences in the energy transmission due to types of exposure, sinusoidal vibration showing higher transmission of energy to the hand-arm system than random vibration, especially at higher frequencies.

The influence of biodynamic factors on the mechanical impedance of the hand and arm.

The purpose of this study was to investigate the mechanical impedance of the human hand-arm system during exposure to random vibration under various experimental conditions and to evaluate statistically whether these experimental conditions have any influence on magnitude and phase of the mechanical impedance. A further aim was to compare the obtained results with other investigations where sinusoidal excitation has been used. The mechanical impedance was estimated in ten healthy subjects during exposure to random vibration, with a constant velocity spectrum within the frequency range 4-2000 Hz, by use of a specially designed laboratory handle. In the study, the influence of various conditions, such as vibration direction (Xh, Yh, Zh), grip force (25-75 N), feed force (20-60 N), frequency-weighted acceleration level (3, 6, 9, 12 m/s2) and hand and arm posture (five flexions, two abductions) were studied. The outcome showed that the vibration direction and the frequency of the vibration stimuli have a strong significant influence on the impedance of the hand. An increased vibration level resulted in a significantly lower impedance for frequencies over 100 Hz. Increase grip and feed forced led on the other hand to an increased impedance for all frequencies. With regard to hand and arm posture, the results show that the flexion and abduction had a significant contribution for frequencies below 30 Hz. Furthermore, the influence of some of the studied variables had a non-linear effect on the impedance but also differed between different exposure directions. It was concluded, moreover, that the vibration response characteristics of the hand and arm differ, depending whether the signal is a discrete frequency signal or a signal consisting of several frequencies.

Mechanical impedance of the human hand-arm system subject to sinusoidal and stochastic excitations

The biodynamic response of the human hand-arm system subject to sinusoidal and stochastic excitations is characterized by using the driving point mechanical impedance technique. The driving point impedance measured under different test conditions revealed significant influence of grip force and the excitation frequencies on the human hand-arm response. The hand-arm response characteristics due to sinusoidal and random excitations varied notably at certain frequency bands suggesting the nonlinear behavior of the hand-arm system. The results revealed peak inter-subject variations of 20–40%, while the peak intra-subject variations are observed to be in the range of 3–5%. This paper also proposes a new method to develop grip force dependent hand-arm vibration (HAV) models such that the strong dependence on the grip force may be accurately characterized. A three degrees-of-freedom (DOF) model developed for this purpose correlated well meeting the overall patterns of the measured data at different grip forces.

Driving-point mechanical impedance of the human hand-arm system: synthesis and model development

A synthesis of the measured values of human male hand-arm impedance characteristics reported in the literature has been performed. The driving-point mechanical impedance data of the human hand-arm grasping a vibrating handle has been compared to highlight the various similarities and differences among the data. Unexplained differences among the results of various studies, conducted independently under nominally equivalent measurement conditions, led to the exclusion of outliers from the analysis. The most probable values of impedance phase and magnitude are defined by lower and upper envelopes of the mean values of the accepted data sets. The mean of the data sets, together with the smoothened envelopes, are used to define the target and range of idealized values of the X h, Y hand Z hcomponents of impedance in the 10–1000 Hz frequency range. A pooling of results from different studies suggests that there is a small dependence of the X hcomponent of impedance magnitude on the hand grip forces. The dependence of the phase of the corresponding impedance component on the hand grip force, however, is insignificant. There is insufficient data from independent sources to establish a dependence of other components of impedance on the hand grip and thrust forces. A four-degrees-of-freedom, lumped parameter model is derived to fit the target impedance magnitude and phase values using a constrained optimization algorithm. The predicted values correlate well with the target values in the selected frequency range.

Vibration transmission characteristics of the human hand-arm and gloves

A test methodology using a laser-based vibration sensor is proposed to evaluate the vibration isolation performance of the commercially available anti-vibration and general purpose industrial hand gloves. The vibration transmission characteristics of the human hand-arm system are investigated through measurement of vibration transmitted to the fingers, knuckle and the wrist in the 10–500 Hz frequency range, under different magnitudes of grip forces and vibration excitations. The vibration attenuation performance of nine different gloves is investigated through measurement and analysis of the vibration response of the coupled hand-glove system. The vibration response characteristics are utilized to propose two- and three-degrees-of-freedom (DOF) lumped parameter linear models of the hand and hand-glove systems, respectively. A comparison of the vibration transmissibility response of the proposed models with the measured data revealed reasonable correlation in the frequency range of interest. The results of the study further revealed that the gloves do not yield effective attenuation of vibration caused by the hand-held power tools.

Forces in the hand-arm system: Investigations of the problem of left-handedness

With the exception of few investigations, left-handed individuals have not been considered in the ergonomic design of products and places of work. About 15% of the population is left-handed. There is, therefore, a big need for ergonomic data for lefthanders. The importance of such data is also demonstrated by the fact that the percentage of lefthanders in the population will continue to increase in the future. In this paper, maximum operational force data of the human hand-arm system are provided. Results of the investigations are: (a) Lefthanders have nearly the same maximum operational force in both hand-arm systems; (b) The values for the maximum static force, recorded in norms, are also valid for lefthanders; (c) Righthanders are less universally employable.

Dynamic Response Analysis of Human's Hand-Arm Vibration System and Identification of joint Spring by Experiments.

This paper presents a two-dimensional dynamic analysis and experiments on the human hand-arm system with various configurations under strong and weak gripped conditions, subjected to sinusoidal acceleration. The direct integration method is adopted, and joint spring and damping parameters have been determined by partial optimization technique with a least squares approach, in which the discrepancy between the theoretical and the observed is iteratively corrected in a multistep manner so that at first the gap for wrist responses is minimized, then followed by the gap for the elbow, and finally the gap for the shoulder. Finally, a more simplified model for the hand-arm system with reduced joint parameters is proposed and its adequacy is verified through simulation. It is shown that the spring and damper of each joint do not depend on their shape configuration, and that phase, response and joint parameter are strongly influenced by the grip condition.

An improved biomechanical model for simulating the strain of the hand-arm system under vibration stress

In order to define relationships between the vibration stress and the strain of the human hand-arm system a biomechanical model was developed. The four masses of the model representing the hand, the forearm and the upper arm were connected by dampers and springs in two perpendicular directions. Simulating muscle activity, damped torsion springs were included additionally. The motions of the model were described by a differential matrix equation which was solved by using a ‘transfer matrix routine’ as well as by numerical integration. Thus, functions with harmonic or transient time courses could be selected as an excitation. The simulated vibrations were compared with those of other hand-arm models. The forces and torques transmitted between the masses, and the energy dissipated by the dampers were computed for several combinations of exciter frequencies and accelerations. The dependence of torques upon excitation agreed fairly well with the behaviour of the arm muscles under vibration as described by various investigators. At frequencies above 100 Hz the energy was dissipated mainly by the dampers between the masses near to the exciter. Transferring this result to the hand-arm system it shows that at high frequencies energy is dissipated by the hand and its palmar tissues and this might be one cause for the incidence of vibration-induced white finger disease.

Mechanical impedance of the human hand-arm system

The mechanical impedance of the human hand-arm system was measured within the frequency range of 20–1500 Hz. A handle, specially designed for such measurements, was used. The studies were carried out on eight healthy male subjects during different experimental conditions defined by three different hard-arm postures, hand grip forces (25–75 N) adopted by the subjects, the amplitude (27–53 mm/ s rms; 1.4–2.8 g at 80 Hz) and direction of the vibration stimuli. The outcome shows that the mechanical impedance of the hand-arm system depends on the frequency of the vibration stimuli. Above 200 Hz, the impedance, in general, increases quite rapidly, from about 150 Ns/m up to about 500 Ns/m at 1500 Hz, with the frequency. At lower frequencies, however, various shapes of the impedance curves were found which were most pronounced between different hand-arm postures. For the transverse direction, the impedance increased from about 50 Ns/m at 20 Hz to maximum about 100 Hz followed by a slight decrease. For the proximal-distal direction the impedance decreased from about 150 Ns/m at 20 Hz to minimum at about 100 Hz. More firm hand grips, as well, as higher vibration levels, resulted in higher impedance magnitudes for frequencies above about 100 Hz. Remarkably enough, for lower frequencies an almost opposite relationship was found. Furthermore, the results indicate a non-linear relationship between mechanical impedence and the studied experimental variables. Therefore, prior to setting up future standards, the mechanical properties of the hand-arm system should be taken into careful consideration.

Mechanical impedance of the human hand-arm system : R. Lundström and L. Burström 1988. (8 pages, 3 figures, 0 tables, 25 references) (in English)

Mechanical impedance of the human hand-arm system : R. Lundström and L. Burström 1988. (8 pages, 3 figures, 0 tables, 25 references) (in English)

Mechanical energy absorption in human hand-arm exposed to sinusoidal vibration.

A possible basis for risk assessment of human exposure to vibration when using hand-held tools may be to determine the amount of mechanical energy that is absorbed by the hand-arm system. The aim of this investigation was to study the absorption of mechanical energy in the human hand-arm system during exposure to sinusoidal vibration within the frequency range of 20 to 1500 Hz. A handle, specially designed for this type of experiments, was used during the measurements. The influence of various experimental conditions, such as three different hand-arm postures, grip force (25-75 N) and vibration levels (27-53 mm/srms), were studied on eight subjects. The outcome clearly shows that the energy absorption properties of the human hand-arm system are more or less dependent on all of the experimental conditions studied, but mainly to the frequency of the vibration stimuli. Furthermore, the results indicate a non-linear relationship between the energy absorbed and all other variables studies.

Time dependence and non-linearity of the impedance of the human hand-arm system while exposed to intense vibration.

The object of the investigation was to find out possible non-linearities and dependencies of the impedance of the hand-arm-system on the exposure time. The measurements were made on four male test persons, with the vibrations being introduced parallel to the forearm axis and in a standing position with the arms stretched. The vibration accelerations were between 11 m/s2 and 36 m/s2, and the measuring handle had a weight of only 48 g. The impedance decreases in dependence on time at maximum spanning force without pressing force. After 1 min of exposure time, values of about 55% are reached at 40 Hz and values of about 80% at 20 Hz. The impedance with pressing force of 100 N without spanning force increases with time, most distinctly at 25 Hz. No influence of the vibration intensity could be seen. The compression-tension quotient was introduced as characteristic for the non-linearity. It is dependent on the frequency, the vibration acceleration and, with large vibration accelerations, also on the exposure time. The quotient is 1 ... 1.5 at vibration accelerations up to 10 m/s2, and 3 ... 4 at vibration accelerations up to 36 m/s2 and after 3 to 5 min exposure time.

Draft for Development: Guide to the evaluation of exposure of the human hand-arm system to vibration: B.S.I. 1975 British Standards Institution D D43. (10 pages, 2 figures, 1 table)

Draft for Development: Guide to the evaluation of exposure of the human hand-arm system to vibration: B.S.I. 1975 British Standards Institution D D43. (10 pages, 2 figures, 1 table)