Page 388 - Mechatronics with Experiments

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FIGURE 6.44: Various load cells using strain gauges for force and torque measurement.

The other alternative for strain-gauge based force/torque sensor is to mount the strain
gauges directly over the shaft on which we want to measure the force/torque. In some
applications, it is not possible to install a load cell. Force or torque on a shaft must be
measured without significantly changing the mechanical design. Figure 6.45 shows such
force and torque sensing using four strain gauge pairs on a shaft. Notice that most force and
torque sensors use symmetrically bonded strain gauges to reduce the effect of temperature
variations and drift of the strain gauge output.
There are two inherent assumptions in the stain-gauge based force/torque sensing:
1. The strain in the material is small enough such that the deformation is in the elastic
range, and that
1 1 F
= = (6.136)
E E A

Strain
gauges F
T
F
Strain
gauges Solid
2 1
circular
45° shaft
Strain 2
Strain gauges 3 4 1 X
gauges
Y

T
F

(a) (b) (c)
FIGURE 6.45: Force and torque measurement on a shaft or beam using strain gauges directly
mounted on the part.