Inspection method, inspection apparatus, and polarization method for piezoelectric element

Abstract

A method for inspecting a piezoelectric element includes first-inspection-signal application step of applying to the piezoelectric element a first inspection signal Vp( 1 ) having a first predetermined voltage waveform; first-characteristic-value measurement step of measuring, as a first characteristic value, an electrical characteristic value of the piezoelectric element after application of the first inspection signal; second-inspection-signal application step of applying to the piezoelectric element a second inspection signal Vp( 2 ) having a second predetermined voltage waveform and an electrical power greater than that of the first inspection signal; second-characteristic-value measurement step of measuring, as a second characteristic value, the electrical characteristic value of the piezoelectric element after application of the second inspection signal; and anomaly determination step of determining whether or not the piezoelectric element is anomalous on the basis of a value corresponding to the difference between the measured second characteristic value and the measured first characteristic value.

1 . A polarization method for a piezoelectric element, comprising the steps of:
 (a) polarizing the piezoelectric element by applying a pulse-shaped voltage of a first magnitude to the piezoelectric element; and   (b) polarizing the piezoelectric element again by applying a pulse-shaped voltage of a second magnitude higher than said first magnitude to the piezoelectric element.   
   
   
       2 . The method of  claim 1 , further comprising additional polarizing steps with the magnitude of the pulse-shaped voltage increasing with each successive step. 
   
   
       3 . The method of  claim 1 , wherein the pulse-shaped voltage includes a basic waveform which increases from zero to a predetermined voltage value and then decreases from the predetermined voltage value to zero. 
   
   
       4 . The method of  claim 1 , wherein the pulse-shaped voltage has a basic waveform which increases from zero to a predetermined voltage value, remains at the predetermined voltage value for a first period, decreases from the predetermined voltage value to zero, and then remains at zero for a second period, the first period being longer than the second period. 
   
   
       5 . The method of  claim 3 , wherein the basic waveform is a voltage waveform in which at least one of an increasing time, which is a time required to increase from zero to the predetermined voltage value, and a decreasing time, which is a time required to decrease from the predetermined voltage value to zero, substantially coincides with a resonance period of the piezoelectric element. 
   
   
       6 . The method of  claim 4 , wherein the basic waveform is a voltage waveform in which at least one of an increasing time, which is a time required to increase from zero to the predetermined voltage value, and a decreasing time, which is a time required to decrease from the predetermined voltage value to zero, substantially coincides with a resonance period of the piezoelectric element. 
   
   
       7 . A polarization method according to  claim 5 , wherein the increasing time and the decreasing time have the same length and substantially coincide with the resonance period. 
   
   
       8 . A polarization method according to  claim 6 , wherein the increasing time and the decreasing time have the same length and substantially coincide with the resonance period.