Difference between revisions of "Human Vibration"

The OROS Body Vibration tool allows users to evaluate the effect of vibration on the human body according to standards ISO 2651 and ISO 5349. These standard define measurement practice and vibration signal analysis to evaluate the effect on health and and comfort of environmental and equipment vibrations on the Human body.<br>

The ISO 2651 describe the effect on health and comfort of vibration on the whole-body in transportation system, and the ISO 5349 the effect on health of vibration on hands and arms when manipulating machine-tools or vibrating objects. In the following, we will see how to use OROS to evaluate these effects.<br>

Once downloaded, you can unzip the folder and lunch the installer program Setup_OROS_BodyVibration_Tool_vXX.exe. Follow the step of the program to properly install the software.<br>

The program will be installed in "C:\OROS\Programs\ExternalTools". Shortcuts are created on the main desktop, in the Windows Start program and in the "Link" repertory of NVGate. By that way you can directly run the program from NVGate.

Studies of the effect of vibrations on the human body suggest that parts of the body don't have the same response to vibrations as others, and will be more sensitive to specific frequencies and transient component of vibration signal. In order to represent the sensitivity of the human body, ISO standards define time-weighting that must applied to the signal according to the environmental conditions. The following part shows how to apply time-weighting filters to your signal using the toolkit.  

To calculate the raw weighted signal, simply select the filters you want in the "Time signal filters" section :  

This indicator is the [[NVGate_Time_Domain_Analysis#Available_results|peak amplitude]] of the vibration signal. It represent the maximal amplitude of the weighted signal. This indicator can be obtained in NVGate by [[NVGate Post Analysis|post-analysing]] the weighted signal with the [[NVGate Time Domain Analysis|TDA plugin of NVGate]].

This indicator is the [[NVGate_Time_Domain_Analysis#Available_results|Crest Factor]] of the vibration signal. It represent the importances of the transient event in the signal as the ratio of the maximal Peak amplitude over the RMS level for the weighted signal. This indicator can be obtained in NVGate by [[NVGate Post Analysis|post-analysing]] the weighted signal with the [[NVGate Time Domain Analysis|TDA plugin of NVGate]].

The MTVV Tau is the integration time, expressed in seconds. This value can be edited before the calculation, but the ISO 2631 recommand to use 1 second. Therefore this is the default value of this parameter.

This metric is the Motion Sickness Dose Value, used to evaluate the ride comfort in in-vehicle measurement. It is expressed in m.s^(1.5).<br>

<math>D_k</math> is the acceleration dose. It is use to evaluate the effect of vibrations on the human spine, and calculated as the 6th root of the sum of the peaks in the acceleration signal raised at the 6th power. it is expressed in m/s². Peaks are defined as the absolute maximum of the acceleration signal between two zeros crossing. In the Z direction, only the positive peak will be considered, were all positive and negative peaks are used for the X and Y directions. <br>

Assessing the affect of the vibration on human spine most is important when dealing with transportation vehicular, especially from driver seat. for a better evaluation, the ISO 2631-5 advises calculating the daily acceleration dose, defined as : <br>

You will then need to enter the reference time you want to use to estimate the parameters on a greater duration. This duration must be entered in seconds. The default value is 288500 second, corresponding to a 8 hour measurement:<br><br>

Human vibrations are transmitted to the human body over a reasonable amount of time. This transmission mainly happens in vehicles during transportation, in buildings, and when using vibrating equipment and tools, such as electric drills, blowers. Since the last century, studies have shown that vibrations can have many affect on the human body, from discomfort and transport sickness to serious health issues, including blood flow disorder to muscular and rheumatisms.<br>

Measurement procedures for whole-body vibration evaluation are described in ISO2631. This type of vibration will mainly occur in transportation and in the workplace when working with big machinery. Therefore, the evaluation of the vibration will be carried out on the part supporting the human body, like backside and feet for a seated person and feet for a standing person.  Sensors must be placed to assess vibration to these specific points. Measurement must be carried on the complete system. Meaning the user must be present during the measurement and operate the machine/vehicle as usual. The following picture, extracted from the standard, gives indication of the orientation of the sensors : <br>

For each point, the vibration must be measured in the three directions: X, Y and Z. As different weighting will be used for each direction, it is really important that each sensor is oriented according to the same directions. The Z direction must always used in the direction of the human spine.<br>

* reduce the Sampling rate, as frequency bandwidth for Whole-body vibration will note exceed 1kHz.

* Split each sensor over several files

Please contact OROS customer care team for advices.

Measurement procedures for hand-arm vibration evaluation are described in the ISO 5349. This type of vibration is transmitted to the body by the hands and the amrs when using hand-tools and equipment, holding a vibrating object (like the steering wheel in a vehicle), or feeding a machine (wood cutting or turning).<br>

Here, the direction of the sensor is not important, however, at least two directions must be acquired at each point in the direction perpendicular to the handle axis. The most important part is to measure vibration at the contact point of the hand and the tool. Specific adaptor can be used to hold the accelerometer with the handle.  

Using the OROS tool kit, long signals file can be take a lot of time to analyze. In order to analyze signal files longer than 30 minutes, we advise to : <br>

* reduce the Sampling rate, as frequency bandwidth for Whole-body vibration will note exceed 1kHz.

* Split each sensors over several files

Please contact OROS customer care team for advices.