Psion Teklogix Vehicle-Mount Computer 8590 User Manual

D.4.1  Approximate Solution For Elastomer Spring Selection

This model applies to the oscillatory mass at the device's center of gravity. This lies 
around 120 mm above the mounting surface of the group of springs and also 
displaced from it. To determine the spring constant for an individual elastomer 
spring, the leverages and arrangement of the springs (here in a triangle) must also be 
considered.
Furthermore, each of the 4 elastomer springs connected in parallel must deliver one 
third of the total spring constant, i.e., 78 N/mm / 3 = 26 N/mm.
To simplify matters, of the 6 possible degrees of freedom we will only consider 
those with the greatest deflection in the case of the 8580. In other words: We 
observe the display as it oscillates towards or away from us (a combination of 
rotational and longitudinal oscillation).
Comparative measurements for precisely the arrangement displayed in Table-top 
attachment with elastomer springs diagram on the previous page:
Attachment (construction of the mounting bracket, quantity and position of the 
elastomer springs) show that the individual spring must be stiffer by a factor of 25 
for the mathematical model stated above to be applied.

As a result, this model gives a value of 26 N/mm x 22.5 = 585 N/mm for the 
required single spring constant.

Since 

ω² = c / m, we obtain the following relationship: 

 

Where: 

 

m 

= oscillatory mass  

= 5  kg 

 

f

e

   = natural frequency  

= 20 Hz 

 

c 

= spring constant in N/mm 

/

78

039

,

0

1000

²

4

2

2

=

⋅

⋅

≈

⋅

⋅

≅

π