Driving device for piezoelectric element

A driving device for driving a piezoelectric element having first and second terminals, comprising:

• power supplying means:
• a coil having a first terminal electrically connected to the first terminal of said piezoelectric element, and a second terminal electrically connected to said power supplying means;
• first switching means interposed between said power supplying means and the second terminal of said coil for selectively connecting said power supply means to and disconnecting said power supply means from said coil;
• second switching means selectively rendered ON and OFF, said second switching means electrically connecting the second terminal of said coil to the second terminal of said piezoelectric element when said second switching means is ON, thereby forming a resonance circuit when said piezoelectric element and said coil;
• connecting means for connecting the second terminal of said coil to said power supplying means to allow a current to flow from the second terminal of said coil to said power supplying means;
• and
• control means for controlling said first and second switching means, wherein said control means controls said first switching means to render ON to instruct displacement of said piezoelectric element and further controls said first switching means to render OFF and said second switching means to render ON to instruct restoration of said piezoelectric element from a displaced condition, and wherein said control means controls said second switching means to render OFF after expiration of a predetermined period of time from a time when said second switching means is rendered ON to allow electrical energy retained in said piezoelectric element to appear in said coil and feed back the electrical energy to said power supplying means through said connecting means and further controls said second switching means to again render ON after said second switching means is rendered OFF to release electric charges in said piezoelectric element produced when a stress is imparted to said piezoelectric element at the time of restoration, said control means includes time measuring means for measuring the predetermined period of time based on an inductance of said coil and a capacitance of said piezoelectric element and said control means controls said second switching means to render ON when said time measuring means indicates expiration of the predetermined period of time.