E-Handout 8
ET
ME360 S2014
Torque  measurement
 
R. Larson
                                                                              

    

Larson Engineering has plans to market an in-line torque monitor for use with an electric drill. The prototype design concept uses an instrumented hollow steel cylinder between the drill output shaft and the drill chuck.  Power (i.e.Torsional moment) is transferred from the motor to the drill chuck through the cylinder.  Circuit connections are made through slip rings, and torque is displayed on a small digital display attached to the drill body. 

The prototype unit is 2.000 long, 1.250 diameter X 0.030 wall thickness aluminum cylinder (E=10 X 106 psi) and has two strain gages (R = 350 ohms, F=2.05) mounted at +/- 45 to the cylinder axis. Gage leads are connected to a Wheatstone bridge circuit with input voltage supplied from the drill battery so that ei = 14.4 Volts, DC. Fixed resistors (Ro=350 ohms) complete the circuit. 

 

A.)  Determine the torque sensitivity deo/dT (milli-volts/inch-pound) for this design. Assume torsion input only; no compressive load or temperature changes exist.  

B.)  What would be the effect, in terms of circuit voltage output and in terms of indicated Torque, if a compressive load of 25.0 lbf is applied during torque application? (i.e. the operator leans on the drill during a drilling operation.) Explain your answer.

 

Solutions:

For part a), I chose to do a parametric study by assuming a Moment value and then solving for the eout that would result... plotted values and found slope of the line via simple rise/run.