Driving device for piezoelectric element

Claim 2

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; first switching means interposed between said power supplying means and the second terminal of said coil and selectively rendered ON and OFF to selectively supply electrical energy from said power supplying means to 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 with said piezoelectric element and said coil; connecting means for allowing the electrical energy to return 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 the 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, wherein said predetermined period of time is defined by π/3 (LC) 1/2 where L is an inductance of said coil and C is an electrostatic capacitance of said piezoelectric element.

Claim 3

The driving device according to claim 1, wherein said control means includes time measuring means for measuring the predetermined period of time and wherein said control means controls said second switching means to render ON when said time measuring means indicates expiration of the predetermined period of time.

Claim 4

The driving device according to claim 2, wherein the predetermined period of time is determined based on an inductance of said coil and a capacitance of said piezoelectric element.

Claim 5

The driving device according to claim 1, wherein said control means waits another predetermined period of time from a time when said first switching means is rendered ON until said first switching means is thereafter rendered OFF so that a sufficient amount of charges are accumulated in said piezoelectric element.

Claim 6

The driving device according to claim 4, further comprising a first closed loop including said coil and said first switching means for allowing a current to continuously flow in said coil until said first switching means rendered OFF.

Claim 7

The driving device according to claim 5, further comprising third switching means having a first terminal connected to said power supplying means, a second terminal connected to the first terminal of said piezoelectric element and a third terminal connected to said control means, and a second closed loop including said coil and said power supplying means, wherein said control means controls said third switching means to render ON when said first switching means is rendered OFF, and wherein a current is supplied to said piezoelectric element through said third switching means if charges retained in said piezoelectric element are wasted and a current flowing in said coil is allowed to flow in said second closed loop.

Claim 8

The driving device according to claim 6, wherein said control means controls said third switching means to render OFF after expiration of yet another predetermined period of time from a time when said third switching means is rendered ON.

Claim 9

The driving device according to claim 6, wherein said control means controls said second switching means to render ON after said third switching means is rendered ON so that a current resulting from the charges accumulated in said piezoelectric element is flowed in a closed loop consisting of said coil and said second switching means, whereby loss of electrical energy is not caused.

Claim 10

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.

Claim 11

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.

Claim 12

The driving device according to claim 9, wherein said control means waits another predetermined period of time from a time when said first switching means is rendered ON until said first switching means is thereafter rendered OFF so that a sufficient amount of charges are accumulated in said piezoelectric element.

Claim 13

The driving device according to claim 10, further comprising a first closed loop including said coil and said first switching means for allowing a current to continuously flow in said coil until said first switching means rendered OFF.

Claim 14

The driving device according to claim 11, further comprising third switching means having a first terminal connected to said power supplying means, a second terminal connected to the first terminal of said piezoeletric element and a third terminal connected to said control means, and a second closed loop including said coil and said power supplying means, wherein said control means controls said third switching means to render ON when said first switching means is rendered OFF, and wherein a current is supplied to said piezoelectric element through said third switching means if charges retained in said piezoelectric element are wasted and a current flowing in said coil is allowed to flow in said second closed loop.

Claim 15

The driving device according to claim 12, wherein said control means controls said third switching means to render OFF after expiration of yet another predetermined period of time from a time when said third switching means is rendered ON.

Claim 16

The driving device according to claim 13, wherein said control means controls said second switching means to render ON after said third switching means is rendered ON so that a current resulting from the charges accumulated in said piezoelectric element is flowed in a closed loop consisting of said coil and said second switching means, whereby loss of electrical energy is not caused.