A frequency signal control circuit for a vibration type motor apparatus, which uses as a driving force a vibration generated by application of a frequency signal to an electro-mechanical energy conversion element thereof, inhibits a shift operation of the frequency signal to a lower frequency when a...http://www.google.com.au/patents/US5495152?utm_source=gb-gplus-sharePatent US5495152 - Frequency signal control circuit and vibration type motor apparatus using same
