Any simple structure : this book, a table, a door, a building, can be excited at a particular frequency which is known as its natural or resonant frequency. If vibration is applied to the structure at or near this frequency then it will vibrate at a higher intensity than that applied to it. This amplification is known as resonance. (Indeed this effect can also occur if the original vibration input is situated close to, but not actually touching, the structure-this is how the sopranos can sometimes shatter glass.) At other frequencies the opposite of resonance can occur, so that the body structure absorbs and so reduces the input intensity. This process is known as damping or attenuation.

The human body is extremelly complex structure which is composed of different organs, bones, joints and muscles. Each of these parts, both individually or together, can be affected in the ways described above. At some frequencies, therefore, they might vibrate at higher intensities than the vibrations applied to them whereas at others they could absorb and attenuate the inputs. Because the resonance, then, body movements can sometimes become difficult for the operator to control whereas, at other frequencies, the vibration energy absorbed by the body during attenuation may be enough to cause structural damage.

The resonance effects of a particular system, for example the hand-arm complex, the head-neck complex, or the whole body itself, can be measured by comparing the vibration intensity of the system both at the point of stimulation and at the point of ‘exit’ for different frequencies. For example, to consider the resonance characteristics of the whole body, vibration measuring devices (accelerometers) could be placed at the feet (entry) and the top of the head (exit) of a standing person. The resonant frequencies, then, are those at which the ‘exit’ intensities exceed the ‘input’ intensities, i.e. when the exit : input intensity ratio is greater than 1. If the ‘transmissibility’ ratio is less than unity the system is absorbing (damping) the vibration.

Performance Effects Of Vibration

Because body parts tend to vibrate in sympathy with vibrating machinery either nearby or on which they may rest, the effects of vibrations on performance occur mainly in terms of reduced motor control. This might be control of a climb (causing, for example, reduced hand steadlines) or of the eyeballs (causing fixation difficulties and blurring). Little evidence exists to suggest the vibration can affect central, intellectual processes.

Visual Performance Effects Of Vibration

A clear perception of an object will only be perceived if a stable image falls on the retina. A moving figure stimulates different set of receptors in the retuna, producing a signal of overlapping and confused images. This is clearly likely to cause difficulty in detecting much of the object’s detail, particularry if the retinal image oscillates with a relativity large amplitude.

Altough a fair amount of work has been carried out to investigate visual vibration effects, it is difficult to draw too many conclusions about the types and levels of vibration that affect visual performance. This is because different investigators have used different tasks to measure visual performance (O’Briant and Ohlbaum, 1970). Because these different tasks require subjects to perform different activities it would be difficult to relate them to each other or to any standard performance criteria.

There are three combinations of observer and object vibration that can result in a moving image being perceived. First, if the objects alone is vibrated; second when only the observer is vibrated; and third when both the observer and the object are vibrated. In this third case the degree of blurring will depend not only on the nature of the vibration experienced but on the phase relationship between the two moving bodies. The effect of these aspects will be considered separately.

Labels: Work Design Environment

Definitions

Vibration may be defined simply as any movement which a body makes about a fixed point. This movement can be regular, like the motion of a weight on the end of the spring, or it can be random. The vibration experienced from machinery is usually a very complex, but regular, motion. Using appropriate analysing techniques, any complex motion can be analysed in terms of a number of simple components. This type of analysis-Fourier Analysis-is outside the bounds of this book but can be found in the most texts dealing with vibration theory.

With vibration being defined in this simple way, it follows that a body can vibrate in a number of different directions, although the International Standards Organization (1974) suggests that any movement should be defined and measured in terms of three orthogonal components : ‘x’-front to back : ‘y’-side to side; and ‘z’-up/down. Using these coordinates, a person jumping up and down, for example, would be vibrating in the z direction. If the same person was rotating about an axis from shoulder to shoulder (for example, tumbling face-forwards from a roof) then the body would be vibrating in the x and z axes in the same time. Finally, a weightless astronout in space may rotate uncontrollably and might be vibrating in all three axes together. For most experimental purposes, however, the effects of vibration are normally considered in one axis only-and this has generally been in the vertical (z) direction.

Types of vibration :

- Sinusoidal : influenced by regular vibration.

- Random : influenced by irregular vibration and the vibration cannot be predicted, ussually it comes from the real world tools.

The types of vibrations based on affected location consist of:

- Whole body vibration : there are three kinds i.e., vertical vibration, horizontal, and lateral vibration.

- Vibration in certain location: on the shoulder part and fingers affected by hand tools.

The reactions caused by vibration are:

- Physiology : depending on frequency and intensity.

- Work performance reaction : depending on frequency, duration, body support, angle, age.

Once the direction of the motion has been determined, the amount of vibration is defined in terms of two parameters : its ‘speed’ and ‘intensity’.

The ‘speed’ of a vibrating body is expressed in terms of its frequency of movement-simply the number of times the body, the weight on the end of a spring for example, completes one cycle movement (i.e. from its fixed reference point to its higest point, to its lowest point and finally back to its reference point) within a spesific time priod (usually 1 second). The faster the body vibrates, therefore, the more cycles that occur per second. The normal unit of frequency in the Hertz (Hz) where 1 Hz = 1 cycle per second.

Vibration intensity is normally expressed in terms of the maximum amount the body moves from the fixed point-usually in distance for amplitude (in cm or in mm). More recently acceleration units have been used to define vibration intensity. These are conventionally expressed in ‘g’ unit (1 g being the amount of acceleration needed to lift a body off the earth’s surface); although the convention hase been changed slighty in recent years to use the metric units of meter per second² (1 g = 9.81 ms^-2).

Each of these parameters is related, thus ;

Acceleration in 'g' unit :

Where f is the vibration frequency and a is the vibration amplitude.

Conversion Table of displacement, velocity, and acceleration :

Labels: Work Design Environment

One of the important factors for work environment and able to give satisfaction and high productivity for employee is a good lighting. For instance, in a mill division, a good lighting will make a safe work place and support work to see things and also reduce mistakes. Efficiency of an operator is determined by constancy in seeing and working. A good lighting can increase work effectiveness and can give the bigger safety.

Many concepts, terms, and units relate to the measurement of illumination. The basic theory applies to a point source of light (such as a candle) of a given luminous intensity, measured in candelas (cd). Light emanates spherically in all direction from the source. The amount of light striking a surface or section of this sphere is termed illumination or illuminance and is measured in foot-candles (fc). Some of that light is absorbed and some of it is reflected (for translucent materials, some is also transmitted), which allows humans to “see” that object and provides a perception of brightness. The amount reflected is termed luminance and is measured in foot-Lamberts (fL). It is determined by the reflective properties of the surface, known as reflectance.

The characteristics of good lighting are having:

1. Enough ray/light

2. The ray/light is not temporarily or cause a glare

3. There is no incisive contrast

4. The bright of light (Brightness)

5. Light distribution, shadow and light radiating/spreading

6. Color

The good lighting is one of the factors to give good sight condition. There are some other factors that influence the power to see. Some of them are related to work physical factor and work place, beside the other aspect like weariness/fatigue and speed in give reaction.

Labels: Work Design Environment

Labels: Work Design Environment

Labels: Work Design Environment

Fatigue

Fatigue can be defined as the decreasing process of efficiency, working performance, and the decreasing of physical strength to do such activity. This fatigue, if not considered immediately, will accumulate from many factors which can cause stress for human body. The fatigue resulted from non-optimality in designing the work method will bring into psycological or even physiological effects.

Energy Resource

*Aerobe Respiration Reaction:

C6 H12 O6 + 6O2------> 6CO 2+ 6H 2O + Energy (674 Kal)

The final result of ATP which has been formed from aerobe respiration of 1 molecule of glucose is: 2 ATP (glycolysis result) + 2 ATP (Kreb cycle result) + 34 ATP (electron transfer result) = 38 ATP

*Anaerob Respiration Reaction:

C6H 12O ----->6CO2 + Energy + Lactic Acid

In the anaerobe respiration the glycolysis process happens as in the aerobe one, but the piruvat acid been formed will not have citrate acid cycle because there is no oxygen, and the number of ATP is 2.

Labels: Fisiology

Metabolism process is a process which results the energy required for doing the physical work. In this process, food nutrients will react with oxygen inhaled, burnt, and results heat and mechanical energy. The amount of energy resulted/consumed is declared in Kilo Calories (Kcal) or Kilo Joule (KJ).

The energy for muscle activity is gained from ATP which is next formed into ADP. ATP is reformed as of the energy resulted from glucose. To avoid the decreasing of blood glucose that caused by respiration in order to result ATP, then the reserves of glycogen is being formed into glucose.

Glycogen----->Lactacidogen -------->Glucose + lactic acid

Lactic Acid will be moved to Hepar (liver) to be formed into glucose. The piles of lactic acid in the muscles will cause fatigue, stiffness, even muscle cramp.

Labels: Fisiology

Energy Consumption

Try to formulate the relation between energy and heart rate searched by the quantitative approach of relation between heart rate and energy with the regression analysis. Regression form of energy and heart rate relation is square regression with the following equation:

Where: Y = energy (kilo/minute)

X = heart rate (beats/minute)

Then it is equalized in mathematic equation as follows:

KE = Ey1 – Ey0

Where:

KE = energy consumption for the certain activity / Kcal

Ey1 = energy expenditure at the certain working time/ Kcal

Ey0 = resting energy expenditure / Kcal

Rest Period (rp) :

t = 60 minutes

W = biggest value of Y

S = Average value of energy expenditure

Recovery Period:

E = KE = Energy consumption during the work

Labels: Fisiology

Another tools for body evaluation is RWL (Recommended Weight limit) Method. There’re defference variable .

VM if lifting upon 69 cm use VM =1-0.0132(V-69)
VM if lifting under 69 cm,use VM = 1-0.0145(69-V)
AM for asimetric factor if 0<=A<=30 use AM=1-(0.005 A) AM for asimetric factor if 30<=60 use AM=1-(0.0031 A) AM for asimetric factor if A>60 use AM=1-(0.0025 A)

can comparism with another formulation :
VM if lifting by Indonesian People use VM=1-0.00326 I V-69 I
Or be side (ethnic group) VM=1-0.03 I V-75 I
AM = 1-0,0032A

Many defference formulation Bio evaluation in one method use another way ,I’ve been learning Biomechanic to get answer all about this so if u have answer tell me another refrence to strong your arguement .

Labels: Biomechanic

Difference Test is used for examine two sample of comparative hypothesis which correlated if data have the shape of Ordinal. We must have done of normalitiy test to know data distribution before we done of difference test.If Data normal so you can using t test,if’nt wilcoxon test (Walpole, 1986).if our sample are difference subject so we can use compare mean by independent-sample T test, If our sample are same subject we can use compare mean by Paired Sampled T-Test.

Steps testing on t-test :
1.Hipotesis
H_{0 :} µ_o = µ_{1 : There's not difference weight score before and after research}
H_{1 :} µ_o ≠ µ_{1 : There's not difference weight score before and after research}

2.Determining of degree Significant
Degree significant has use is 5% or 0.05, with df = n-1

3.Comparism great probability by degree significant
if probability (sig) > 0.05 HO excapted
if probability (sig) <>

Labels: Difference Test

Labels: Ergonomi

QEC (Quick Exposure Checklist)

QEC merupakan suatu metode untuk penilaian terhadap risiko kerja yang berhubungan dengan gangguan otot di tempat kerja. Metode ini menilai gangguan risiko yang terjadi pada bagian belakang punggung, bahu/lengan, pergelangan tangan, dan leher. QEC membantu untuk mencegah terjadinya WMSDs seperti gerak repetitive, gaya tekan, postur yang salah, dan durasi kerja. (Stanton, 2004) .Penilaian pada QEC dilakukan pada tubuh statis (body static) dan kerja dinamis (dynamic task) untuk memperkirakan tingkat risiko dari postur tubuh dengan melibatkan unsur pengulangan gerakan, tenaga/beban dan lama tugas untuk area tubuh yang berbeda (Li dan Buckle, 1999). Konsep dasar dari metode ini sebenarnya adalah mengetahui seberapa besar exposure score untuk bagian tubuh tertentu dibandingkan dengan bagian tubuh lainnya. Exposure score dihitung untuk masing-masing bagian tubuh seperti pada punggung, bahu/lengan atas, pergelangan tangan, maupun pada leher dengan mempertimbangkan ± 5 kombinasi/interaksi, misalnya postur dengan gaya/beban., pergerakan dengan gaya /beban, durasi dengan gaya/beban, postur dengan durasi, pergerakan dengan durasi (Brown & Li , 2003). Salah satu karakteristik yang penting dalam metode ini adalah penilaian dilakukan oleh peneliti dan pekerja, dimana faktor risiko yang ada dipertimbangkan dan digabungkan dalam implementasi dengan tabel skor yang ada (Li&Buckle, 1998).

Untuk modul QEC dapat didonlot disini

Untuk kuisioner QEC dapat didonlot disini

Untuk software QEC dapat didonlot disini

Labels: Ergonomi

ErgoEASER

Software ErgoEASER dikembangkan oleh Pacific Northwest Laboratory untuk Departemen Energi Amerika Serikat. ErgoEASER Ergonomic Analysis Tool dimaksudkan untuk memberikan kesadaran akan pentingnya ergonomi pada areal kerja. VDT Workstation Analysis pada software ErgoEASER adalah sebuah metode yang dikembangkan dalam bidang ergonomi dan dapat digunakan secara cepat untuk menilai posisi kerja dan tata letak (layout) stasiun kerja berkomputer. Teknologi ergonomi tersebut mengevaluasi postur/posisi kerja seorang operator computer dan faktor layout stasiun kerjanya, termasuk ukuran dimensional kursi. Penilaian postur kerja metode ini dengan cara pemberian analisis apakah pekerjaan beresiko menimbulkan ketidaknyamanan atau tidak. Jika pekerjaan berpotensi menimbulkan ketidaknyamanan maka akan ditampilkan pula rekomendasi untuk perbaikan perancangan ulang (redesign) pekerjaan tersebut.

• Untuk modul ErgoEASER dapat didonlot disini
• Untuk Software ErgoEASER dapat didonlot disini

Labels: Ergonomi

OWAS (Ovako Working Posture Analiysis System)

OWAS merupakan suatu metoda yang digunakan untuk mengevaluasi dan menganalisis sikap gerak tubuh pekerja/operator pada saat bekerja. Metoda ini perkembangannya dimulai tahun tujuh puluhan diperusahaan penghasil besi baja Ovako Oy Finlandia (sekarang Fundia Wire), kemudian dikembangkan oleh Karhu dan Nasman serta kawan-kawannya dan Laboratorium kesehatan buruh Finlandia (Institut kesehatan kerja). Pada kurun waktu 1977 Karhu dan kawan-kawan memperkenalkan metode ini untuk pertama kalinya, tetapi dalam disertasi pada kurun waktu 1985 dari Stoffert menyempurkannya dengan metode evaluasi secara detail. Rata-rata tingkat kesamaan dan ketelitian dalam mengukur perbedaan sikap orang adalah 90% atau lebih, testnya dilakukan pada 20 atau lebih jenis industri/perusahaan (Karhu, 1981).

untuk modul WinoWas dapat didonlot disini

untuk software WinOwas dapat didonlot disini

Labels: Ergonomi