Parameters Associated with the Assessment of Whole Body Shock and Vibration Exposure

Following are parameters listed in ISO 2631-Pt 1 that are used to assess exposure to whole body shock and vibration:ETURN

ISO Weighted rms  Acceleration Value, a_w:

where a_w(t) is the instantaneous ISO weighted acceleration value as a function of time, and T is the integration time. a_w values are used for whole body vibration exposures that do not contain shock events.

ISO Weighted 4th Power Vibration Dose Value, VDV:

VDV values are used for whole body vibration exposures that contain shock events.

Daily Vibration Exposure Value, A(8):

where T is the total exposure time during an 8 hour work day. A(8) values are a_W values normalized to an 8-hr workday.

Overall Seat Air Bladder Performance for Large Material Handling Vehicles  with no Vehicle Suspension System Used to Offload Container Ships

Table 1 shows a summary of results for the measured ISO weighted rms and VDV acceleration values for the ErgoAir^® seat air bladder and the existing air-ride suspension seat system in two different large material handling vehicles with no vehicle suspension system. The vehicles are used to offload large containers from container ships. They were driven over predefined courses within a shipyard that had significant bumps and potholes. The surfaces over which the vehicles were driven were typical of the shipyard.

The EU Human Vibration Directive forbids whole body vibration exposure above an ISO rms weighted acceleration value of 1.15 m/s² and an ISO weighted VDV value of 21 m/s^1.75 for an 8-hour workday. According to the results displayed in Table 3, these values would be exceeded for the vehicles that were tested. This will require a less than 8-hour work shift for driving these vehicles to be in compliance with the EU Human Vibration Directive. Locking out the air-ride suspension in the seat system and replacing the seat cushion with the ErgoAir^® seat air bladder will make it possible for the vehicle operators to work a full 8-hour work shift.

Figure 1 shows a plot the measured vibration transmissibility for an ErgoAir^® seat air bladder for a seat occupant exposed to a combined repeated shock and vibration input in the z-direction (vertical). Transmissibility values are given for the 1/3 octave frequency bands of 1.25 to 100 Hz. The weight of the seat occupant was 150 lb_f. The figure indicates seat occupant-seat bladder system had a resonance frequency in the 4 Hz 1/3 octave frequency band.

Vibration transmissibility, TR, is obtained from:

where a_input is the acceleration measured between the seat pan and the seat air bladder, and a_response is the acceleration measured between the seat air bladder and the buttock of the seat occupant. Figure 2 shows a corresponding plot of the measured percent vibration reduction associated with the seat air bladder.

Percent vibration reduction is obtained from:

Figure 1

Overall Seat Air Bladder Performance for Large Military Off-Road Wheeled Vehicle  with a Soft Vehicle Suspension System