Cutting force monitoring using strain guage

Force monitoring

An electric circuit, that is fit for estimating the exceptionally little changes in resistance comparing to strain. This circuitry is utilized to quantify the strain with fortified opposition strain gauges. Typically, four strain gauge components are electrically associated with structure a Wheatstone bridge circuitry. 

A Wheatstone bridge is a separated bridge circuit utilized for the estimation of static or dynamic electrical opposition. The yield voltage of the Wheatstone bridge circuit is as milli volts (mv) yield per volt input. The Wheatstone circuit is likewise appropriate for temperature compensation. The numerical representation of the Wheatstone bridge, if R1, R2, R3, and R4 are equivalent, and a voltage, Vin , is applied between focuses A and C, at that point the yield between focuses B and D will show no expected distinction. Notwithstanding if R4 is changed to some esteem which doesn't rise to R1, R2, and R3, the bridge will become unequal and a voltage will exist at the yield terminals. In an alleged G-bridge setup, the variable strain sensor has opposition Rg, while different arms are fixed worth resistors. The sensor, in any case, can involve one, two, or four arms of the Wheatstone bridge, contingent upon the application. The all out strain, or yield voltage of the circuit (Vout) is equal to the contrast between the voltage drop across R1 and R4, or Rg.


Strain Gauge location

Example 1

The reason for this model is to ascertain the load force P, as appeared in Figure 2, with the assistance of two strain gages introduced on a rectangular pillar. Remembering that this pillar could be either the cutting tool holder, or it tends to be the cutting tool shank, and the edge or tip of the cutting tool is the main point of activity of the loal P. The two strain gages are locked in on the outside of the cantilever pillar as appeared in the figure. These strains mounted on a superficial level are in pressure when the load P is applied toward the finish of bar. These strain gages must be associated with a Wheatstone bridge in the manner R and R2, or R1 and R3, as appeared in Figure 1, to finish the bridge circuit other two resistors must be added, remembering that these resistors have same ostensible estimation of resistance as that of strain gages. The reason for doing so is to keep the bridge be as equilibrium as could be expected under the circumstances (Vο= 0) when the gages are unreformed.


Example 2

The purpose of dynamometer in dynamometer based system was to measure the cutting force. So dynamometer was installed in tool shank so that it can measure the cutting force involve in the turning process. The best feature of this process is that the dynamometer can be installed very easily on the tool shank. Other than this its customization is very easy as the data transmission happen through wireless setup. In order to avoid thermal effect of cutting operation and to increase the sensitivity of the apparatus, the installation of strain gauge is done away from the tip of the cutting tool cutting tip. This helps protect the dynamometer from damages when the tool failure occur. In order to achieve an amplified strain in results most strain gauges are placed at the hole of the tool shank or at the place of high stress concentration. This is done to avoid compromising the stiffness of the tool shank.


In above mention circuit of dynamometer based setup, the volte value provided by the Wheatstone Bridge is first amplified about 200 times more the original one and then it is transferred to frequency from voltage by an IC. Then these signals are delivered to an IR Emitter diode that is placed at the back side of shank of tool. After this stage the signal which are in frequency form are then again converted into voltage once again and that voltage is proportional to the strain value of the tool. The offset value of the voltage which is due to the unbalancing of the bridge is considered as the final output value.

Example 3

At the point when load P and Q are applied toward the end rectangular cross sectional zone of the instrument holder, minutes Mp and Mq and powers. Which bring with strain in strain gauges which are mounted on the rectangular cross sectional territory of the cutting tool holder. The circular drill is made at the focal point of cross sectional region, this is where strain gauges are introduced. There are two reason for doing this. First increment the affectability of the dynamometer, second design is to keep the solidness of hardware holder for all intents and purposes unaltered. 

Thinking about the accompanying conditions for this model: 

a) Strain gages with an ostensible resistance estimation of R, 

b) Strain gages of segments 1 and 2 (base and excellent condition) a full bridge with yield voltage V01, 

Considering that the instrument holder is made of a decent thermally conductive material, for example, aluminum, remembering the reality given above it is sensible suspicion that the temperature of all the strain gages is nearly the equivalent. Therefore, variety in temperature influences the affectability of all the strain gages similarly, dropping its impact on the last estimation. Extra strain gages must be introduced to quantify the pivotal power R,