A low frequency vibration type washing machine is disclosed that is capable of detecting the range of linear reciprocating movement of its drive shaft to control the vibration range of its low frequency oscillating vibrator to be constant, and sensing water level in its washing tub to control the water...http://www.google.com/patents/US5452594?utm_source=gb-gplus-sharePatent US5452594 - Low frequency vibration type washing machine and method
