No-backlash control system by two-motor drive (The analyses of backlash occurrence mechanism)

Abstract

We analyze backlash occurrence mechanism of a no-backlash drive control technique in which two motors drive a load axis, as one is for a plus direction and another is for a minus direction, into the simulation and the experiment. We derive a condition that the backlash occurs easily when the load inertia is more than the driving system inertia, and that the backlash becomes hard to occur when the load inertia exceeds a certain value. We conclude that the condition to be the easiest to cause the backlash is that, a natural frequency of the driving system is equal to a natural frequency of the load, where the former natural frequency is calculated from the motor inertia, the gear ratio and stiffness of the drive line and the latter one is calculated from the load inertia and stiffness of the drive line. In this condition, Gramian, which measures the contribution of each natural frequency to the input/output (the position reference / the transmission torque of the gears between the driving axes and the load axis) also becomes the maximum. Since these two natural frequencies are practically determined by mechanical dimensions regardless of the controller gain, we need to separate these natural frequencies in mechanical design of the no-backlash driving system.