“…The control system keeps the stator and the friction material in the ultrasonic friction reduction by controlling the driving circle frequency, π π’ [28,29], such that the equivalent friction coefficient, π π€ Μ
Μ
Μ
Μ
, (Equation (S.1) in the Supplementary Material) is smaller than the sliding friction coefficient, π 0 . The sliding friction force, π π ππππ , and the maximum static friction force, π π ππππ₯ , in the case of ultrasonic friction reduction can be obtained by multiplying both sides of Equation (S.1) by the pre-pressure, πΉ π , as follows: The control system keeps the stator and the friction material in the ultrasonic friction reduction by controlling the driving circle frequency, Ο u [28,29], such that the equivalent friction coefficient, Β΅ w , (Equation (S1) in the Supplementary Material) is smaller than the sliding friction coefficient, Β΅ 0 . The sliding friction force, f slidc , and the maximum static friction force, f scmax , in the case of ultrasonic friction reduction can be obtained by multiplying both sides of Equation (S1) by the pre-pressure, F c , as follows:…”