Abstract: In a reciprocating rotor device such as a scanning galvanometer, a bearing assembly consisting of a rheological bearing coupler interposed between the rotor shaft and the bearing support structure or housing, where the rheological bearing coupler is relatively stiff during constant-velocity portions of rotor rotation, assuring adequate geometrical precision of the rotor within the rotor housing during the scanning phase. When loaded beyond a design load threshold by acceleration-induced moments causing lateral or asymmetrical force applied between the shaft and the bearing support structure during changes in rotor speed, becomes relatively compliant or resilient, absorbing a portion of the load at the expense of momentary axial misalignment of the rotor, then returning to original shape and realigning the rotor to it's correct precision axial position when the acceleration forces are abated.