ROLLING FRICTION TORQUE IN MICROSYSTEMS FOR DRY AND LUBRICATED CONDITIONS

The authors developed a dynamic model for an inertial rotating disc sustained by three microballs and determined analytically relations for rolling friction torque in the contacts between steel microballs and races by using two hypothesis: (i) rolling friction torques not depending on the speed for dry conditions and (ii) rolling friction torque having a linear dependence with the speed for lubricated contacts. Using an original microtribometer was verified the two hypothesis and was determined the rolling friction torque for very low normal loads. The values between 1.9 mu Nmm to 7.4 mu Nmm have been obtained for the rolling friction torque when the normal load and rotational speed have variations between 8.68 mN to 33.2 mN and 30 rpm to 210 rpm, respectively. In lubricated contacts important increasing of the rolling friction torques with values between 8 mu Nmm to 1150 mu Nmm was obtained, depending on rotational speed.