Measuring Range/Introduction of Force
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5.
Measuring Range/Introduction of Force
5.1
3-Component Force Measurement Using a Dynamometer
The design of a dynamometer, consisting of four 3-com-
ponent force sensors and common base and cover plates,
ensures that the forces applied exert no moments on the
individual force sensor. The force sensor can therefore be
loaded up to the maximum defined measuring range (mo-
ment-free).
With regard to the zero point of a dynamometer, however,
a force vector whose line of action does not go through
this zero point will produce a moment. Moments M
x
and
M
y
cause some of these sensors to be subjected to an addi-
tional load in the F
z
direction and the other sensors to a
reduction in load in the F
z
direction. Moment M
z
results in
a loading of the sensors in the F
x
, F
y
plane.
For a 3-component force measurement with a dynamome-
ter consisting of four 3-component sensors, the output sig-
nals (each of F
x
, F
y
and F
z
) of the four sensors are summed.
However, the sum of the four sensors always shows the
correct value irrespective of the force application point.
A 3-component dynamometer measures
the three com-
ponents of all the resulting forces acting on the dyna-
mometer and their direction but not their position in
space.
Depending on the location of the force application point,
the load is distributed over all four sensors. However, alter-
natively, an individual sensor can receive the main part of
the force. If the force is applied far outside the dynamome-
ter then, according to the law of the lever, an individual
sensor can experience a multiple of the force to be meas-
ured. For applications of this kind, the load on an individual
sensor must be accurately calculated.
The following fule of thumb applies to the measuring
range of a dynamometer:
If the force application point of the resulting force vec-
tor is within a pyramid consisting of the cover plate sur-
face and a height corresponding to the shorter side of
the cover plate, then the maximum measuring range of
an individual force sensor applies for the entire plate.
